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Evaluator last updated February 18, 2025.

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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.

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At a glance

Input typeInformational text
Supported grades3–12
RubricSAP ↗‘s Qualitative Text Complexity Rubric for Informational Text ↗
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 usedGPT-4o
Temperature0

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Getting started

Follow the Quickstart to start using this evaluator:
Access method
Evaluators PlaygroundView in the Learning Commons Platform ↗
SDKTypeScript ↗
Python notebookView in GitHub ↗
PromptsView in GitHub ↗

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Inputs

InputDescriptionRequired
Target grade levelEnables grade context evaluationYes
Text typeInformational text
optimal length: 100–200 words (max ~1,200 characters)		Yes

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Output

FieldDescription
AnswerComplexity score (“Slightly complex”, “Moderately complex”, “Very complex”, or “Exceedingly complex”)

See Interpreting results for grade-specific criteria
ReasoningExplanation of the rating based on identified sentence features and grade context

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Interpreting results

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Grade 3

Complexity scoreHow to use
Slightly complexSimple, straightforward language and sentence structures

Meets 2+ of the following criteria:
  • Sentence type: Typically > 60% simple sentences
  • Sentence length: Typically < 12 average words per sentence
  • Subordination: Typically < 25% of sentences have subordinate clauses
Moderately complexMix of simple and more complex sentences:
  • Sentence type: Typically 40 - 60% simple sentences
  • Sentence length: Typically 12 - 16 average words per sentence
  • Subordination: Typically 25 - 45% of sentences have subordinate clauses
Very complexMore elaborate sentences with multiple clauses and ideas:
  • Sentence type: Typically < 40% simple sentences
  • Sentence length: Typically 16 - 19 average words per sentence
  • Subordination: Typically > 45% of sentences have subordinate clauses
Exceedingly complexDense with very long, intricate sentences and high subordination

Meets 2+ of the following criteria, including 1+ from “Structural density”:

Structural density
  • Subordination: Typically > 50% of sentences have subordinate clauses
  • Multiple subordination: Typically > 12% of sentences have 1+ subordinate clause
  • Syntactic complexity: Typically > 15% compound-complex sentences


Length
  • Sentence length: Typically > 19 average words per sentence
  • High concentration of very long sentences: Typically > 15% of sentences have 30+ words

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Grade 4

Complexity scoreHow to use
Slightly complexSimple, straightforward language and sentence structures

Meets 2+ of the following criteria:
  • Sentence type: Typically > 55% simple sentences
  • Sentence length: Typically < 13 average words per sentence
  • Subordination: Typically < 30% of sentences have subordinate clauses
Moderately complexMix of simple and more complex sentences:
  • Sentence type: Typically 40 - 55% simple sentences
  • Sentence length: Typically 13 - 17 average words per sentence
  • Subordination: Typically 30 - 50% of sentences have subordinate clauses
Very complexMore elaborate sentences with multiple clauses and ideas:
  • Sentence type: Typically < 40% simple sentences
  • Sentence length: Typically 17 - 22 average words per sentence
  • Subordination: Typically > 50% of sentences have subordinate clauses
  • Multiple subordination: Typically > 8% of sentences have 1+ subordinate clause
Exceedingly complexDense with very long, intricate sentences and high subordination

Meets 2+ of the following criteria, including 1+ from “Structural density”:

Structural density
  • Subordination: Typically > 60% of sentences have subordinate clauses
  • Multiple subordination: Typically > 15% of sentences have 1+ subordinate clause
  • Syntactic complexity: Typically > 20% compound-complex sentences


Length
  • Sentence length: Typically > 22 average words per sentence
  • High concentration of very long sentences: Typically > 15% of sentences have 30+ words

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Grades 5-12

Complexity scoreHow to use
Slightly complex>= 50% simple sentences

Exception: Moderately Complex if >= 50% simple sentences AND >= 20% compound sentences

Important: NEVER includes advanced complex sentences
Moderately complexPrimarily 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.

May contain many simple sentences, compound sentences, and/or basic complex sentences, as well as 1 - 2 advanced complex sentences.
Very complex3+ advanced complex sentences

Exception: Exceedingly Complex if >= 65% advanced complex sentences
Exceedingly complex>= 65% advanced complex sentences

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Accuracy and validation

This evaluator is provided as Early access. Comprehensive accuracy measures are not yet available. Validation testing is ongoing.
We assessed performance against an expert-annotated dataset of CLEAR Corpus ↗ texts — ~480 for Grade 3 and ~480 for Grade 4. Accuracy has been most extensively validated on Grades 3–4. We are still evaluating the performance for grades 5-12.
MetricDescriptionResult
Expert agreementThe percentage of evaluated examples where at least one expert agreed with the evaluator’s rating during review testing.53% agreement for Grade 3
54% agreement for Grade 4
Accuracy within one-levelThe percentage of evaluator ratings that fall within the same complexity level or one level away from the of expert annotators’.94%
Baseline comparisonHow the evaluator’s accuracy compares to a simple, unrefined prompt.26% more accurate
For more information on our validation process, see Accuracy.

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Evaluator release history

DateChanged
February 18, 2026Added grades 5-12.
September 23, 2025First release