Grammar mistakes that cost points in TOEFL Writing

By the AIL teaching team, Melbourne · Updated 4 November 2026 · 8 min read

Short answer

The grammar mistakes that cost most in TOEFL Writing are question word order (including indirect questions), missing articles, subject-verb agreement, plural uncountable nouns, run-on sentences and wrong word forms. The ETS rubric for a 5 allows almost no errors beyond typos, while a 3 shows "some noticeable" errors, so a few repeated mistakes can cost a point.

In the 2026 TOEFL iBT Writing section, grammar affects all three tasks. Build a Sentence is marked right or wrong, so one misplaced word loses the item. In Write an Email and Write for an Academic Discussion, the difference between a 4 and a 3 is often the number of noticeable errors, not the quality of the ideas. The good news is that most candidates repeat the same three or four mistakes, which makes them easy to find and fix.

What the ETS rubric says about grammar

ETS publishes separate scoring guides for the email and the discussion post, both on a 0–5 scale. As of November 2026, the language descriptors read like this (Academic Discussion wording):

Score	What it says about errors
5	"Almost no lexical or grammatical errors other than those expected from a competent writer writing under timed conditions (e.g., common typos or common misspellings or substitutions like there/their)"
4	"Few lexical or grammatical errors"
3	"Some noticeable lexical and grammatical errors in sentence structure, word form or use of idiomatic language"
2	"An accumulation of errors in sentence structure, word forms or use"

The email guide uses almost the same language, and adds "social conventions" such as politeness and register.

Two things follow from this. First, ETS does not expect perfect writing. A typo or a their for there will not move you down. Second, the step from 4 to 3 is about errors becoming "noticeable". In practice that means a reader sees the same kind of mistake more than once. Three missing articles in a 120-word post are noticeable. One is not.

Grammar is also only part of the score. A 5 needs well-elaborated ideas and "precise, idiomatic word choice" as well. But grammar is the part you can improve fastest, because the errors are predictable.

Build a Sentence: word order is the whole task

In Build a Sentence you put chunks of words in order to make a reply to a short message. Our Build a Sentence guide covers the method. The grammar that decides most items is:

Direct questions need the auxiliary before the subject: When does the workshop start? not When the workshop starts?

Indirect questions go back to normal statement order: Do you know when the workshop starts? not Do you know when does the workshop start? This is the single most common error we see, in Build a Sentence and in emails.

Frequency adverbs go before the main verb but after be: She usually walks to campus. She is usually early.

Time and place usually go at the end, place before time: I left my notes in the lab yesterday.

If the fixed words in the reply end with a question mark, check whether the sentence is a direct question or an indirect one starting with Could you tell me or Do you know. That choice decides the word order of everything after the question word.

The eight mistakes we see most in emails and posts

These come from reviewing practice-test responses at AIL. Each one is small. Repeated three or four times, each is enough to make errors "noticeable".

1. Indirect questions with question word order

Emails often ask for information politely, and that is where this error appears.

✗ Could you tell me where can I collect the form?
✓ Could you tell me where I can collect the form?

2. Missing or extra articles

Use a/an for one of something mentioned for the first time, the when the reader knows which one, and no article for general plural or uncountable nouns.

✗ I am writing about seminar on Friday. Seminar room was too small.
✓ I am writing about the seminar on Friday. The seminar room was too small.
✗ The students need the more time for the research.
✓ Students need more time for research.

3. Subject-verb agreement after long subjects

The verb agrees with the head noun, not the nearest noun.

✗ The number of students who use the shuttle buses have increased.
✓ The number of students who use the shuttle buses has increased.
✗ One of my classmates think that...
✓ One of my classmates thinks that...

4. Uncountable nouns made plural

Information, advice, equipment, research, feedback, homework, furniture, evidence and knowledge have no plural.

✗ I would appreciate any advices or informations you can give.
✓ I would appreciate any advice or information you can give.

5. Run-on sentences and comma splices

Two complete sentences joined with only a comma is an error in sentence structure, which the rubric names directly.

✗ I agree with Daniel, volunteering teaches skills that lectures cannot.
✓ I agree with Daniel. Volunteering teaches skills that lectures cannot.
✓ I agree with Daniel, because volunteering teaches skills that lectures cannot.

6. Fragments starting with because or which

The opposite problem: a clause that cannot stand alone, written as a sentence.

✗ Universities should give credit for volunteering. Because it builds real experience.
✓ Universities should give credit for volunteering because it builds real experience.

7. Wrong word form

Noun, verb, adjective and adverb forms are easy to mix up when writing fast.

✗ This policy would be very benefit for first-year students.
✓ This policy would be very beneficial for first-year students.
✗ It is important to communicate effective with the group.
✓ It is important to communicate effectively with the group.

8. Tense shifts inside a story

When you give an example from your own experience, stay in the past.

✗ Last year I join a tutoring program and I learn how to explain ideas clearly.
✓ Last year I joined a tutoring program and learned how to explain ideas clearly.

Check one discussion post freePaste your writing and get an estimated 0–5 score with corrections in about 30 seconds. No account needed.

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An example: the same post at two levels

The professor's question (original): Some universities give academic credit to students who complete volunteer work in the community. Should all universities do this? Why or why not?

Version with errors (about 3 on the rubric):

I agree with Daniel that universities should give credit for volunteering, it gives students experiences that is useful for their career. For example, last year my cousin volunteer at a food bank and she learn how to organise a team of twenty people. She said me that this was more useful than any of her lecture. Because she had to solve real problems every day. Also employers values this kind of the experience. So I think universities should do it.

The ideas are clear and the example is specific. But there are nine noticeable errors: a comma splice, experiences that is, volunteer and learn in the present, said me, any of her lecture, a because fragment, employers values, and the experience.

Corrected version (moving towards 4–5):

I agree with Daniel that universities should give credit for volunteering, because it gives students experience that is directly useful in their careers. Last year, for example, my cousin volunteered at a food bank, where she learned how to organise a team of twenty people. She told me this was more useful than any of her lectures, since she had to solve real problems every day. Employers also value this kind of experience, as it shows they can take responsibility outside a classroom. For these reasons, I think every university should offer this option.

The content is almost the same. The score difference comes from accuracy, plus one added clause of explanation about employers. That is typical: fix the grammar and your existing ideas start to count for more.

A two-minute check before time runs out

You have about 7 minutes for the email and 10 for the discussion post. Save the last 1–2 minutes and check for your own top mistakes, not everything. Read through once for each of these:

Verbs. Does every sentence have one? Does it agree with its subject? Is the tense right for the time you are describing?
Nouns. Is each singular countable noun preceded by a, the, my or similar? Have you made any uncountable noun plural?
Sentence ends. Is there a full stop where two sentences meet? Does any "sentence" begin with because or which and stand alone?
Questions. In an email, does every could you tell me / I was wondering clause use statement order?

Don't use the last 30 seconds to add a new idea. An unfinished new sentence is a guaranteed error.

Practice: correct these sentences

Each sentence has one error. Answers are below.

Do you know what time does the library close on Sunday?
I have attached a evidence of my enrolment.
Each of the proposals have some advantages.
Living on campus help students make friends quickly.
I disagree with Mei, online lectures are harder to concentrate on.
The new timetable was very confused for international students.
Two years ago I start working part-time at a bakery.
I am writing to ask for an extension for my assignment. Which is due on Monday.

Answers: 1. what time the library closes. 2. some evidence (or proof). 3. Each of the proposals has. 4. Living on campus helps. 5. I disagree with Mei. Online lectures... (or because online lectures...). 6. very confusing. 7. I started working. 8. ...for my assignment, which is due on Monday.

If you got four or more wrong, the error types in those sentences are your list for the two-minute check. For more on what else lowers scores outside grammar, see 12 common TOEFL mistakes.

To test this on real posts, paste a discussion post into our free Academic Discussion checker. It gives a 0–5 score and lists corrections from your own text, so you can see which of the eight errors you repeat. The AIL TOEFL iBT® style practice tests also include Build a Sentence and Write an Email, and you can try a free Writing section. These practice materials are written by AIL teachers; TOEFL and TOEFL iBT are registered trademarks of ETS, and AIL's practice tests are not endorsed or approved by ETS.

Find out where you are todayTry a free TOEFL iBT style practice in any skill, then sit a full timed practice test with 1–6 scores in minutes.

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Questions people also ask

Does grammar matter in TOEFL Writing?

Yes. In Build a Sentence, word order is the whole task. In the email and discussion tasks, the ETS rubric for a 4 allows "few" errors and a 3 describes "some noticeable" errors, so repeated small mistakes can cost a full point on a task.

Will spelling mistakes lower my TOEFL Writing score?

Occasional typos are allowed. The top band in the ETS rubric accepts "common typos or common misspellings or substitutions like there/their". Frequent spelling errors that make words hard to recognise are a different matter and count against you.

What is the most common grammar mistake in TOEFL Writing?

In our practice tests, it is question word order, especially in indirect questions like "Could you tell me where can I...". Articles and subject-verb agreement come close behind.

Should I use complex sentences to get a higher score?

Use them when they fit, but not at the cost of accuracy. The rubric rewards "a variety of syntactic structures", and it also counts errors. A post with clear, accurate sentences and a few well-formed complex ones will score better than one full of long sentences that go wrong.

How can I find my own grammar mistakes?

Collect three or four of your past responses and mark every error by type. Most people find that two or three types cover more than half their mistakes. Check for those types specifically in the last two minutes of each task.