REVIEW 4 major objections 5 minor 34 references
Can LLMs Reliably Simulate Real Students' Abilities in Mathematics and Reading Comprehension?
T0 review · 4 major / 5 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read This paper claims that no LLM–prompt combination reliably matches average student performance in mathematics or reading for grades 4, 8, and 12.
desk verdict A valuable, honest empirical study on LLMs as student proxies, but the IRT measurement model has an unresolved inconsistency that weakens the quantitative claims. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing mechanism is the Rasch model from item response theory, a one-parameter model in which the probability of a correct answer depends only on the difference between a test-taker's ability $\theta_i$ and an item's difficulty $b_j$. Item difficulties are fixed from real NAEP students' correct-response proportions via $b_j = \log\left(\frac{1-p_j}{p_j}\right)$, and the population ability scale is pinned by assuming student abilities follow $\mathcal{N}(0,1)$, so the average student sits at $\theta = 0$ and each LLM's percentile rank is $\Phi(\theta_i) \times 100$. This places each LLM as a synthetic examinee on the same scale as real students, with the 50th percentile as the target for an average grade-level student. The second piece of machinery is the set of grade-enforcement prompts (minimal, basic chain-of-thought, and full chain-of-thought) that attempt to steer the model toward that target.
What would settle it
Recompute the analysis with a two-parameter (2PL) or three-parameter (3PL) IRT model fit to the full NAEP item-level response data rather than the logit approximation, and compare each LLM's percentile rank; if models reported as far above the 50th percentile, such as o3-Mini, land near 50 under the alternative model, the alignment failure is a measurement artifact. Alternatively, hold out half of the NAEP items per grade-subject, select the best model-prompt pair on the training half, and test on the held-out half; if the pair's percentile deviation from 50 does not persist, the reported alignment is overfitted to the specific item set.
Extended reading notes
Core claim
The paper's central discovery is that placing 11 LLMs on the same Rasch ability scale as real NAEP students yields a systematic mismatch: in the unenforced condition, strong general-purpose models such as o3-Mini and Qwen2.5-7B score in the high 90s percentile at every grade and subject, far above the average student's 50th percentile, while weaker or domain-mismatched models land closer to 50 only incidentally. Grade-enforcement prompts that instruct the model to behave like an average student shift percentile ranks significantly in some cases, but the direction and size of the shift are model- and prompt-specific: some models overshoot downward, some barely move, and no single model-prompt pair stays within the targeted alignment across mathematics and reading at grades 4, 8, and 12. The authors conclude that faithful grade-level emulation likely requires explicit alignment objectives in training, not just prompting, and they offer proxy-selection guidelines based on grade alignment, developmental ordering, and prompt stability.
Load-bearing premise
The load-bearing premise is that the Rasch model with logit-estimated item difficulties and a standard-normal student ability distribution puts an LLM's percentile rank on a scale where the 50th percentile truthfully represents the average grade-level student; if that scale is biased, the paper's alignment findings could be artifacts of the measurement model.
Editorial extensions
If this is right
- Strong general-purpose models score at the 95th percentile or above on unenforced grade-level items, so without explicit constraint they cannot stand in for average students in any grade or subject.
- Grade-enforcement prompting moves percentile ranks by tens of points in some cases but not in predictable directions, so a prompt that aligns one model on one subject-grade cell cannot be expected to transfer to another.
- A few model-prompt pairs do align with the average student in specific cells, meaning a proxy student can be selected only cell-by-cell, not globally.
- Pedagogically fine-tuned models are no better aligned than general models, indicating that domain fine-tuning alone does not produce grade fidelity.
- Before an LLM is used to pilot test items or train a tutor, it should be checked against the paper's criteria: ability within $\pm 1$ logit of the grade mean, monotonically increasing ability across grades, and stability under grade-enforcement prompts.
Reading between the lines
- The paper's IRT percentile check could be reused as a cheap acceptance test for any new LLM proxy: evaluate it on a small NAEP-like multiple-choice set, compute its percentile, and reject it if it falls outside the chosen band, turning the paper's negative result into a practical screening tool.
- Because the absolute percentiles depend on the normal-ability and logit-difficulty assumptions, the exact numbers may be biased, but the qualitative overshoot pattern would survive re-anchoring because raw accuracies are already far above student means.
- The results connect to the broader finding that persona prompts like 'you are a 4th grader' change superficial behavior more than calibrated ability; a natural testable extension is to measure whether trial-by-trial confidence or error patterns, not just accuracy, move toward a real student's response distribution.
- A direct next experiment would hold out a subset of NAEP items per grade-subject, fit the Rasch model on the training subset, and check whether the best model-prompt pair from the paper maintains its alignment on the held-out subset, a generalization check the paper does not report.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper investigates whether LLMs can serve as reliable stand-ins for average K-12 students by comparing 11 LLMs with NAEP students on 489 multiple-choice mathematics and reading items across grades 4, 8, and 12. The authors calibrate item difficulties from real students' aggregate proportion-correct values using a logit approximation, estimate each LLM's ability via a Rasch-model maximum likelihood fit, and convert the resulting abilities to percentile ranks under a standard-normal ability distribution. They compare unenforced and three grade-enforced prompting strategies and report that strong general-purpose models consistently exceed the average student's 50th percentile, while weaker or domain-mismatched models can align incidentally; they conclude that no evaluated model-prompt pair aligns with the average student across all subjects and grades, and they propose screening guidelines for selecting proxy students.
Significance. The paper addresses a timely and practical question, and the dataset release plus the systematic comparison across 11 models and four prompt conditions are useful contributions to the NLP-for-education community. The qualitative pattern—strong models overshoot and weak models align for incidental reasons—is plausible and likely to survive a corrected analysis. However, the paper's quantitative claims are built on a psychometric calibration that is internally inconsistent (Eq. 2 versus the N(0,1) assumption), and the normative bands in the guidelines contain a numerical labeling error. Because the headline conclusion is expressed in percentile units derived from that calibration, the paper needs a substantial statistical revision before the specific alignment claims can be accepted.
major comments (4)
- [Section 4.1 (Eq. 2) and Section 5.3] The item difficulty estimator b_j = log((1-p_j)/p_j) is not compatible with the student ability model θ~N(0,1) used for the percentile ranks. Under the Rasch model with a standard-normal ability distribution, the population proportion correct is p_j = ∫ σ(θ-b_j) φ(θ) dθ, and solving this convolution for b_j does not reduce to the inverse logit of p_j. The inverse-logit formula instead makes the θ=0 examinee reproduce each item's population proportion exactly, which systematically shrinks the spacing of item difficulties relative to the normal-ability metric. The LLM abilities θ_i estimated by maximum likelihood are therefore on a different scale, and the reported percentile ranks Φ(θ_i) do not describe the LLM's position in the real student ability distribution. Since the headline conclusion in the abstract and Section 6.3 is stated entirely in percentile units, this issue is load-bearing. Please re-estimate item difficulties under the N(0,1) marginal likelihood (or another explicitly fitted ability distribution), provide item-fit diagnostics, and report whether the conclusions survive.
- [Section 5.3 and Figure 2] The normality justification is not about the quantity that matters. The KS tests in Figure 2 are applied to the distribution of item accuracies within each grade and subject, not to student abilities. Thus the text stating that all subsets 'sufficiently follow a normal distribution' cannot be used to support the assumption θ~N(0,1). The N(0,1) assumption is an identification convention, but after using Eq. (2) the item difficulties and the ability distribution are not jointly identified to that convention. The statement that 'the average student has an ability parameter of zero' is therefore an anchor of convenience rather than an empirical benchmark, and the percentile interpretation in Eq. (3) is untested. Please either fit the ability distribution from the available response moments or present the results on the logit scale and add a sensitivity analysis for the assumed ability distribution.
- [Section 6.4] The normative band percentiles are numerically wrong. Φ(±1) = [15.87, 84.13], Φ(±1.5) = [6.68, 93.32], and Φ(±2) = [2.28, 97.72]. The paper labels 6.68–93.32 as 'core ±1', 2.28–97.72 as 'extended ±1.5', and 15.87–84.13 as 'outlier ≥±2', which swaps the bands. This also affects the adjacent claim that GPT-3.5-Turbo 'stayed in the core range with appropriate prompts for most grades': under the corrected core band, the grade-8 math PE of 11.7 is below 15.87 and thus not in the core. Please correct the bands and re-check any statements that rely on them.
- [Section 5 and Table 2] All model ability estimates are point estimates from a single deterministic run per prompt (temperature=0). No standard errors, confidence intervals, or bootstrap replicates are reported, even though each model answers only 61–106 items per cell. Consequently, cells that are a few percentile points from the alignment band are not statistically distinguishable from aligned cells, and the precise statement that 'no evaluated model–prompt pair fits the bill' is stronger than the evidence supports. Please report uncertainty intervals for θ_i and the percentile ranks, and verify the headline conclusion against a reasonable tolerance interval.
minor comments (5)
- [Abstract and Section 6.3] The phrase 'no evaluated model–prompt pair fits the bill across subjects and grades' reads as though no pair is ever aligned, but Table 2 shows several aligned cells (e.g., LLaMA2-13B on grade-8 mathematics). Please state the claim as 'aligned in all six subject–grade combinations' to avoid ambiguity.
- [Algorithm 1] Line 10 contains an extra closing parenthesis: 'πi ← Φ(θi) × 100)' should read 'πi ← Φ(θi) × 100'.
- [Appendix C] There is a typo: 'HunggingFace' should be 'Hugging Face' or 'HuggingFace'.
- [Table 5] Some prompt labels contain spurious spaces (for example, 'G RADEENFORCEDFULLCOT'); please fix the table-generation formatting so the prompt names are rendered consistently.
- [Table 2] The Random Choice row is formatted inconsistently with the rest of the table and does not clearly align with the six subject–grade columns; please restructure that row so each value sits under the correct column.
Circularity Check
No significant circularity: LLM abilities are measured against external NAEP student response data rather than derived from the target conclusion, so the central claim is an empirical finding.
full rationale
The paper's derivation chain is not circular. Item difficulties are estimated from NAEP student response proportions (Eq. 2), which are external inputs; LLM responses are then queried independently under each prompting condition, and each model's ability is estimated by maximum likelihood from its own response pattern. The 'average student' at percentile 50 is an identification convention (theta ~ N(0,1) in Sec. 5.3), not a fitted parameter, so comparing LLM theta estimates to zero is a substantive empirical comparison rather than a restatement of the input. No model parameter is fitted to the alignment outcome and then renamed as a prediction; the Sec. 6.4 proxy-selection guidelines are post-hoc criteria, not derived predictions. Citations to prior work (Benedetto et al. 2024, Embretson and Reise 2000, Bond and Fox 2015) are used for prompts and standard IRT conventions, not as unverified self-citations carrying the argument. The paper does contain legitimate statistical concerns, such as the inconsistency between Eq. 2's logit approximation and the N(0,1) ability scale used for percentiles, and the numerically swapped normative bands in Sec. 6.4, but these are correctness and validity issues rather than circularity. No equation or claim reduces to its own inputs by construction, so the circularity score is 0.
Assumptions & free parameters
free parameters (1)
- Item difficulty set {b_j} (489 items) =
Computed via b_j = log((1-p_j)/p_j) from NAEP p_j
assumptions (3)
- domain assumption Student abilities are standard normally distributed: theta ~ N(0,1).
- domain assumption The Rasch model holds for all NAEP items and the student population.
- ad hoc to paper The logit approximation b_j ≈ log((1-p_j)/p_j) is a consistent estimator of item difficulty under the Rasch model with N(0,1) ability.
Cite this review
Pith. "Pith review of Can LLMs Reliably Simulate Real Students' Abilities in Mathematics and Reading Comprehension?." pith.science (2026). https://pith.science/paper/SQEYJYR3
@misc{pith2026250708232,
author = {Pith},
title = {Pith review of: Can LLMs Reliably Simulate Real Students' Abilities in Mathematics and Reading Comprehension?},
year = {2026},
howpublished = {\url{https://pith.science/paper/SQEYJYR3}},
note = {Machine review of arXiv:2507.08232}
}
read the original abstract
Large Language Models (LLMs) are increasingly used as proxy students in the development of Intelligent Tutoring Systems (ITSs) and in piloting test questions. However, to what extent these proxy students accurately emulate the behavior and characteristics of real students remains an open question. To investigate this, we collected a dataset of 489 items from the National Assessment of Educational Progress (NAEP), covering mathematics and reading comprehension in grades 4, 8, and 12. We then apply an Item Response Theory (IRT) model to position 11 diverse and state-of-the-art LLMs on the same ability scale as real student populations. Our findings reveal that, without guidance, strong general-purpose models consistently outperform the average student at every grade, while weaker or domain-mismatched models may align incidentally. Using grade-enforcement prompts changes models' performance, but whether they align with the average grade-level student remains highly model- and prompt-specific: no evaluated model-prompt pair fits the bill across subjects and grades, underscoring the need for new training and evaluation strategies. We conclude by providing guidelines for the selection of viable proxies based on our findings.
Figures
Figures from the paper (7 more)
Reference graph
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Reviewed August 6, 2026 · model on record in the stance chip above.
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