> ## 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

|                      |                                                                                                                                                                                                                                            |
| :------------------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Inputs**           | Informational text to evaluate and grade level                                                                                                                                                                                             |
| **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) ↗ |

The evaluator was built and validated using the model and temperature below (other configurations will produce different results and may have lower accuracy). The evaluator must be run in two stages — combining them into a single step reduces accuracy.

|                 |        |
| :-------------- | :----- |
| **Model used**  | GPT-4o |
| **Temperature** | 0      |

## 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/sentence-structure.ts) ↗                                                                                                                                                                                                                                                                                                                                                      |
| **GitHub**                | [Python notebook](https://github.com/learning-commons-org/evaluators/blob/main/evals/student-facing-text/ela-reading/sentence-structure/example_notebook.ipynb) ↗<br />Prompts ([`system.txt`](https://github.com/learning-commons-org/evaluators/blob/main/evals/student-facing-text/ela-reading/sentence-structure/system.txt) ↗ and [`user.txt`](https://github.com/learning-commons-org/evaluators/blob/main/evals/student-facing-text/ela-reading/sentence-structure/user.txt) ↗) |

## 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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