> ## Documentation Index
> Fetch the complete documentation index at: https://docs.learningcommons.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Sentence Structure

> Analyze sentence complexity in informational texts, including clause ratios and words per sentence, and get a grade-level complexity rating via LLM.

[Evaluator last updated August 27, 2026.](#evaluator-release-history)

<EarlyAccess isBreaking={false} />

## Overview

The Sentence Structure evaluator assesses the complexity of sentence structure in informational texts relative to a specified grade level:

* Identifies sentence features in the text, including sentence type composition, average words per sentence, subordinate clause ratios, and concepts per sentence.
* Assigns an overall complexity rating using an LLM, combined with statistical thresholds for sentence features.

## At a glance

|                      |                                                                                                                                                                                                                                                                 |
| :------------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Supported grades** | 3–12                                                                                                                                                                                                                                                            |
| **Rubric**           | [Student Achievement Partners (SAP)](https://learnwithsap.org/) ↗'s [Qualitative Text Complexity Rubric for Informational Text](https://learnwithsap.b-cdn.net/app/uploads/2026/04/Qualitative-Text-Complexity-Rubric-Informational.pdf) ↗ (Sentence Structure) |
| **Model used**       | GPT-4o with temperature of 0 <Note>The evaluator was built and validated using this specific model and temperature. Other configurations will produce different results and may have lower accuracy.</Note>                                                     |

The evaluator must be run in two stages — combining them into a single step reduces accuracy.

## Getting started

Follow the [Quickstart](/evaluators/getting-started/quickstart) to start using this evaluator:

| Access method             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| :------------------------ | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Evaluators playground** | [View in Platform](https://platform.learningcommons.org/apps/evaluators/playground) ↗                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| **SDK**                   | [TypeScript](https://github.com/learning-commons-org/evaluators/blob/main/sdks/typescript/src/evaluators/text-complexity/ela-reading/sentence-structure.ts) ↗                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| **Other**                 | [Python notebook](https://github.com/learning-commons-org/evaluators/blob/main/evals/text-complexity/ela-reading/sentence-structure/example_notebook.ipynb) ↗<br /><br /><br />Prompts:<ul><li>[`analysis-system.txt`](https://github.com/learning-commons-org/evaluators/blob/main/evals/text-complexity/ela-reading/sentence-structure/analysis-system.txt) ↗</li><li>[`analysis-user.txt`](https://github.com/learning-commons-org/evaluators/blob/main/evals/text-complexity/ela-reading/sentence-structure/analysis-user.txt) ↗</li><li>[`complexity-system.txt`](https://github.com/learning-commons-org/evaluators/blob/main/evals/text-complexity/ela-reading/sentence-structure/complexity-system.txt) ↗</li><li>[`complexity-user.txt`](https://github.com/learning-commons-org/evaluators/blob/main/evals/text-complexity/ela-reading/sentence-structure/complexity-user.txt) ↗</li></ul><br />Grade-specific rubrics referenced in prompts:<ul><li>[`rubric-grade-3.txt`](https://github.com/learning-commons-org/evaluators/blob/main/evals/text-complexity/ela-reading/sentence-structure/rubric-grade-3.txt) ↗</li><li>[`rubric-grade-4.txt`](https://github.com/learning-commons-org/evaluators/blob/main/evals/text-complexity/ela-reading/sentence-structure/rubric-grade-4.txt) ↗</li><li>[`rubric-grades-5-12.txt`](https://github.com/learning-commons-org/evaluators/blob/main/evals/text-complexity/ela-reading/sentence-structure/rubric-grades-5-12.txt) ↗</li></ul> |

## Inputs

| Input           | Description                                                                        | Required |
| :-------------- | :--------------------------------------------------------------------------------- | :------- |
| **Text**        | Informational text to evaluate<br />10 - 10,000 words (\< 1,200 words recommended) | Yes      |
| **Grade level** | Target student grade level                                                         | Yes      |

## Output

| Field                | Description                                                                                                                                                                                    |
| :------------------- | :--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Complexity score** | Complexity score ("Slightly complex", "Moderately complex", "Very complex", or "Exceedingly complex")<br /><br />See [Interpreting results](#interpreting-results) for grade-specific criteria |
| **Reasoning**        | Detailed, pedagogically appropriate reasoning explaining how the qualitative structure and quantitative sentence statistics combine to produce the chosen complexity level                     |

## Interpreting results

### Grade 3

| Complexity score        | How to use                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| :---------------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Slightly complex**    | Simple, straightforward language and sentence structures<br /><br />Meets 2+ of the following criteria:<ul><li><strong>Sentence type:</strong> Typically > 60% simple sentences</li><li><strong>Sentence length:</strong> Typically \< 12 average words per sentence</li><li><strong>Subordination:</strong> Typically \< 25% of sentences have subordinate clauses</li></ul>                                                                                                                                                                                                                                                                                                                                                           |
| **Moderately complex**  | Mix of simple and more complex sentences:<ul><li><strong>Sentence type:</strong> Typically 40 - 60% simple sentences</li><li><strong>Sentence length:</strong> Typically 12 - 16 average words per sentence</li><li><strong>Subordination:</strong> Typically 25 - 45% of sentences have subordinate clauses</li></ul>                                                                                                                                                                                                                                                                                                                                                                                                                  |
| **Very complex**        | More elaborate sentences with multiple clauses and ideas:<ul><li><strong>Sentence type:</strong> Typically \< 40% simple sentences</li><li><strong>Sentence length:</strong> Typically 16 - 19 average words per sentence</li><li><strong>Subordination:</strong> Typically > 45% of sentences have subordinate clauses</li></ul>                                                                                                                                                                                                                                                                                                                                                                                                       |
| **Exceedingly complex** | Dense with very long, intricate sentences and high subordination<br /><br />Meets 2+ of the following criteria, including 1+ from "Structural density": <br /><br />**Structural density**<ul><li><strong>Subordination:</strong> Typically > 50% of sentences have subordinate clauses</li><li><strong>Multiple subordination:</strong> Typically > 12% of sentences have 1+ subordinate clause</li><li><strong>Syntactic complexity:</strong> Typically > 15% compound-complex sentences</li></ul><br /><br />**Length**<ul><li><strong>Sentence length:</strong> Typically > 19 average words per sentence</li><li><strong>High concentration of very long sentences:</strong> Typically > 15% of sentences have 30+ words</li></ul> |

### Grade 4

| Complexity score        | How to use                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| :---------------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Slightly complex**    | Simple, straightforward language and sentence structures<br /><br />Meets 2+ of the following criteria:<ul><li><strong>Sentence type:</strong> Typically > 55% simple sentences</li><li><strong>Sentence length:</strong> Typically \< 13 average words per sentence</li><li><strong>Subordination:</strong> Typically \< 30% of sentences have subordinate clauses</li></ul>                                                                                                                                                                                                                                                                                                                                                           |
| **Moderately complex**  | Mix of simple and more complex sentences:<ul><li><strong>Sentence type:</strong> Typically 40 - 55% simple sentences</li><li><strong>Sentence length:</strong> Typically 13 - 17 average words per sentence</li><li><strong>Subordination:</strong> Typically 30 - 50% of sentences have subordinate clauses</li></ul>                                                                                                                                                                                                                                                                                                                                                                                                                  |
| **Very complex**        | More elaborate sentences with multiple clauses and ideas:<ul><li><strong>Sentence type:</strong> Typically \< 40% simple sentences</li><li><strong>Sentence length:</strong> Typically 17 - 22 average words per sentence</li><li><strong>Subordination:</strong> Typically > 50% of sentences have subordinate clauses</li><li><strong>Multiple subordination:</strong> Typically > 8% of sentences have 1+ subordinate clause</li></ul>                                                                                                                                                                                                                                                                                               |
| **Exceedingly complex** | Dense with very long, intricate sentences and high subordination<br /><br />Meets 2+ of the following criteria, including 1+ from "Structural density": <br /><br />**Structural density**<ul><li><strong>Subordination:</strong> Typically > 60% of sentences have subordinate clauses</li><li><strong>Multiple subordination:</strong> Typically > 15% of sentences have 1+ subordinate clause</li><li><strong>Syntactic complexity:</strong> Typically > 20% compound-complex sentences</li></ul><br /><br />**Length**<ul><li><strong>Sentence length:</strong> Typically > 22 average words per sentence</li><li><strong>High concentration of very long sentences:</strong> Typically > 15% of sentences have 30+ words</li></ul> |

### Grades 5-12

| Complexity score        | How to use                                                                                                                                                                                                                                                                                                                                                                                                                   |
| :---------------------- | :--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Slightly complex**    | >= 50% simple sentences<br /><br />**Exception:** Moderately Complex if >= 50% simple sentences AND >= 20% compound sentences<br /><br />**Important:** NEVER includes advanced complex sentences                                                                                                                                                                                                                            |
| **Moderately complex**  | Primarily simple and compound sentences, with some complex constructions; can take on any distribution of sentence types as long as there aren't > 2 advanced complex sentences and as long as there aren't so many simple sentences that the text becomes Slightly Complex. <br /><br />May contain many simple sentences, compound sentences, and/or basic complex sentences, as well as 1 - 2 advanced complex sentences. |
| **Very complex**        | 3+ advanced complex sentences<br /><br />**Exception:** Exceedingly Complex if >= 65% advanced complex sentences                                                                                                                                                                                                                                                                                                             |
| **Exceedingly complex** | >= 65% advanced complex sentences                                                                                                                                                                                                                                                                                                                                                                                            |

## Evaluator release history

| Date               | Changed              |
| ------------------ | -------------------- |
| August 27, 2026    | Minor prompt updates |
| February 18, 2026  | Added grades 5-12    |
| September 23, 2025 | First release        |

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