A teacher co-grades a set of ELA essays with a colleague. The AI-graded batch comes back with an average higher than the human-graded batch, and the AI gave 80s, 90s and 100s to essays missing a thesis. Administration still wants the tool department-wide.
That scenario, posted on r/Teachers this week, is the question behind “is AI essay grading accurate.” The short answer: accuracy depends on the rubric and the trait being scored, no independent test of CoGrader, EssayGrader or Brisk was found, and the pattern teachers describe is score inflation on weak essays. AI grading is safest as a drafting aid with the teacher owning the final score.
A spot-check that takes about an hour settles the question for any specific classroom. The rest of this piece covers what the three tools do, what the research supports, what teachers report, and how to run that check.
What CoGrader, EssayGrader and Brisk actually do
The three tools are often grouped together, but they are built differently. CoGrader and EssayGrader are dedicated grading platforms: upload essays, attach a rubric, receive scores and comments. Brisk is a browser extension that works inside Google Docs and similar tools, and teachers describe it mainly as a way to draft feedback comments they then edit.
Pricing below comes from each vendor’s pricing page, checked on 2026-10-21.
| CoGrader | EssayGrader | Brisk | |
|---|---|---|---|
| Free tier | Starter: 150 student submissions per month | Basic: 100 essays per month, 1,000-word limit | Free plan for teachers; page gives no numeric cap |
| Individual paid plan | $15/month billed annually ($19 monthly), 350 submissions | Pro: $14.99/month, 350 essays | Not listed; paid tiers are school and district quotes |
| Higher tiers | Schools & Districts: quote | Premium $34.99/month, 800 essays; district quote | Premium and Intelligence: district quotes |
| Built around | Rubric-based scoring and comments | Batch essay grading | Feedback drafted inside Google Docs |
Free tiers make a classroom-sized trial cheap, so cost is rarely the obstacle. The obstacle is whether the scores can be trusted.
What the published evidence supports
The independent research on large-language-model essay scoring is mixed. A 2025 study from an Italian university group tested five models, including GPT-4, Claude 3.5 and Gemini 2.5, on 67 student essays from a psychology course. It reported human-model agreement that was “consistently low and non-significant,” a tendency to inflate scores for Coherence, and weak consistency when the same model scored the same essay repeatedly (median Kendall’s W below 0.30).
One study does not settle the matter. Results vary by language, rubric and prompt, and other studies report moderate to good agreement on narrower tasks. The finding that carries over to classrooms is the repeat-scoring weakness: a model that gives the same essay different scores on different runs cannot be treated as a measuring instrument without human review.
None of the three tools has an independent accuracy test that could be found. CoGrader is the only one with a published figure. A third-party roundup reports that CoGrader’s own June 2026 report found its scores within one point of Texas state raters on 98.5% of 600 released STAAR responses, with exact agreement on extended essays lower at 72.4%. Another site that compared tools said it found only a qualitative reliability statement on CoGrader’s website, with no number. The report itself could not be located, it is self-published, and it is not peer reviewed. The figure is worth requesting from the vendor, not worth relying on.
What teachers report when they use these tools
Teacher accounts are anecdotal, but they converge on a few specific failure patterns.
Inflation on weak essays. The teacher behind the r/Teachers thread describes regrading five AI-scored papers in a meeting with administrators:
“…it was inflating the grades and making up imaginary feedback that doesn’t actually apply to what the student wrote (i.e. “your thesis did not answer the question” when there was no thesis at all, granting them 2 points higher or 5ish percentage points than if it correctly assessed that there was no thesis).”
Misranking in both directions. Another teacher in the same thread, whose English department had piloted an AI grader, reported the reverse problem alongside the inflation:
“Most of the time kids who wrote very well would be given a 1 or a 2 rating (out of 4) for decent writing. Then the kids who literally just copied and pasted paragraphs from the text they read for the essay received a 4. They stopped mandating it.”
The direction of error is not consistent. A third commenter on the same thread, told to use a specific prompt, found the opposite. Including the earlier drafts’ grades in the prompt pulled the AI’s scores down:
“…the class’s average was a whole letter grade lower (yes, that means most of the students I gave D’s to, the AI wanted to flunk)”
That variability matters more than any single direction. A tool that errs consistently high can be corrected for; one that moves with prompt wording and draft history needs a human check on every batch.
Trait-level unevenness. A teacher on r/ELATeachers who uses Writable’s AI feedback wrote that “most of the time it either lowballs the grade or (with grammar and usage ironically) gives too high of a score.” Another, who uses AI for the rubric score only, said the AI “doesn’t do the best with accuracy” on the content category, so the teacher overrules it.
Generic comments. A parent on r/ELATeachers described reading Brisk comments on a child’s essay:
“Brisk highlighted the first sentence of the conclusion and stated that the writer should restate the thesis in that position. … when I fed his essay into ChatGPT, it delivered the same comments as Brisk.”
The experience is not uniformly negative. A teacher on the same thread who uses Brisk with a premium school license wrote that it “allows me to edit the response before posting anything,” adding “Many times, I change the feedback completely, but it gives me a good starting point.” In a separate r/Teachers thread about grading 150 essays, a commenter wrote that MagicSchool is effective for grading a lot of essays in a short amount of time. The positive reports share a feature: the teacher stays the final grader.
The spot-check that settles it for one classroom
Before relying on any tool, or before answering a mandate, the comparison can be done with the teacher’s own rubric and about ten essays.
- Pick 10 essays across the range: two or three strong, four or five middling, two or three weak. Include at least one with a missing thesis or major component.
- Score them first, blind to the AI. Write down the teacher’s scores before opening the tool.
- Run the AI with the exact rubric the department would use, and run the weakest essays twice to see whether the score moves.
- Compare on three points: the average gap, the rank order (does the best essay still rank first), and whether any comment describes something the essay does not contain.
- Keep the table. A one-page grid of teacher score, AI score, and the time each took is concrete evidence in a meeting, and it is the same method teachers on r/Teachers suggested to each other.
A gap of a few points that runs in a consistent direction can be managed with a rubric adjustment. A rank-order failure or an invented comment is a stronger reason to keep the tool away from final grades.
Our take: use AI for comments, keep the grade human
AI essay graders are the right tool for a narrower job than the one administrators are buying them for. Drafting comment banks, flagging grammar patterns and producing first-draft feedback on early drafts are tasks where the output is reviewed before a student sees it. Final summative scores are a different case, because an inflated 90 on an essay with no thesis tells the student that no reteaching is needed, which is the opposite of what grading is for.
The strongest argument against a grading mandate is not philosophical. It is the regrade table: when administrators see AI and human scores side by side on the same essays, the discussion shifts from preference to measurement. Teachers in the r/Teachers thread described exactly this approach, and one reported bringing evidence of the tool’s errors to administrators after a subject leader pushed AI grading.
The counter-argument is real. Teachers with 150 or more essays and no planning time have a genuine workload problem, and several commenters said students rarely read detailed feedback anyway. For that situation, rubric-based triage, focused feedback on one or two criteria and conference-on-request, all described in the r/Teachers grading thread, solve the time problem without handing the score to a model. Where a tool is adopted anyway, the safest configuration is AI-drafted comments, teacher-assigned scores, and a periodic re-run of the spot-check, since model updates can shift results without notice.
Privacy deserves a check as well. Several teachers raised student-data concerns, and the practical step is to confirm that the tool appears on the district’s approved-software list and that any data-sharing agreement covers student writing. Related guidance on how detection tools perform is in Is Turnitin’s AI Detector Accurate?, and a broader tool comparison is in Best AI Grading Tools for Teachers. Two adjacent decisions are covered in AI report card comment generators and FERPA and Quill vs NoRedInk vs Writable for ELA teachers, and for university-level grading, Gradescope vs Crowdmark.
Frequently Asked Questions
Is AI essay grading accurate?
Accuracy varies by rubric, prompt and trait. Independent studies report low to moderate agreement with human raters, and teachers describe inflated scores on weak essays and harsh scores on strong ones. No independent accuracy test of CoGrader, EssayGrader or Brisk was found. A 10-essay blind regrade is the reliable check.
Can a school require teachers to use AI to grade essays?
Districts can adopt tools and set expectations, but whether a specific mandate holds depends on district policy, union contracts and state rules. A documented side-by-side comparison of AI and teacher scores on the same essays is the most common evidence teachers bring to administrators. The district’s approved-software and data-privacy policies are the first things to read.
Are CoGrader and EssayGrader free?
Both have free tiers as of October 2026. CoGrader’s Starter plan lists 150 student submissions per month and EssayGrader’s Basic plan lists 100 essays per month. Paid individual plans start at $14.99 per month on EssayGrader and $15 per month billed annually on CoGrader. Confirm limits on the official pricing pages, since they change.
Does AI work better for feedback than for scores?
Teacher reports point that way. Comments that the teacher reviews and edits get more positive reviews than final grades assigned by the model, and several teachers describe overriding the AI on content accuracy. Feedback drafting keeps the teacher’s judgment in the loop.
How often should the spot-check be repeated?
At the start of each term and after any announced model or tool update. The research on repeat scoring shows that results can differ run to run, so a one-time check does not guarantee stable behavior.
Keep the grade, borrow the draft
AI essay graders have not earned the final say on a student’s score. The evidence is thin, the vendor claim is self-reported, and teachers describe errors in both directions. The tools earn their place when they draft comments a teacher edits.
A ten-essay regrade, kept as a table, answers the accuracy question for one classroom better than any vendor page. Run it before the mandate, and bring the table to the meeting.
References
- r/Teachers — “Admin wants to mandate using AI to grade essays in ELA” (thread, Oct 2026) — https://reddit.com/r/Teachers/comments/1xab5s3/admin_wants_to_mandate_using_ai_to_grade_essays/
- r/ELATeachers — “Anyone else ethically feel bad about using AI to give writing feedback?” (thread, Nov 2024) — https://reddit.com/r/ELATeachers/comments/1gjwnsc/anyone_else_ethically_feel_bad_about_using_ai_to/
- r/Teachers — “How do you guys manage grading 150 essays?” (thread, Aug 2026) — https://reddit.com/r/Teachers/comments/1vuhntq/how_do_you_guys_manage_grading_150_essays/
- Gaggioli et al., “Assessing the Reliability and Validity of Large Language Models for Automated Assessment of Student Essays in Higher Education,” arXiv:2508.02442 (Aug 2025) — https://arxiv.org/abs/2508.02442
- CoGrader pricing page (checked 2026-10-21) — https://www.cograder.com/pricing
- EssayGrader pricing page (checked 2026-10-21) — https://www.essaygrader.ai/pricing
- Brisk Teaching plans page (checked 2026-10-21) — https://briskteaching.com/plans
- The AI Rankings, “Best AI Essay Graders” (secondary source for CoGrader’s self-reported STAAR comparison; the original report was not located) — https://theairankings.com/best-ai-essay-graders/
