10 Grammar Mistakes That Cost You Points on TOEFL Writing
Even advanced English speakers make these common grammar errors on the TOEFL. These mistakes can drop your score from 5 to 3 on the Write an Email and Academic Discussion tasks, or cause you to lose points on Build a Sentence items entirely. Learn to identify and fix them to boost your TOEFL writing score. (See the visual summary infographic at the end for a quick reference.)
Watch: Common Grammar Mistakes Explained
Video overview of the most common grammar mistakes English learners make
Why Grammar Matters More in TOEFL 2026
The new Build a Sentence task directly tests grammar—if your word order is wrong, you get zero points. For Email and Discussion tasks, "grammatical accuracy" is explicitly mentioned in the scoring rubric. Fix these mistakes to maximize your score.
The 10 Mistakes
Subject-Verb Agreement Errors
The subject and verb must match in number (singular/plural). This is especially tricky with complex subjects or when words come between the subject and verb.
"The group of students are working on the project."
"Everyone have their own opinion."
"The group of students is working on the project."
"Everyone has their own opinion."
Quick Rule:
- • "Group," "team," "class," "family" = singular verb (is, has, was)
- • "Everyone," "someone," "nobody," "each" = singular verb
- • Ignore words between subject and verb when determining agreement
Run-on Sentences & Comma Splices
Two complete sentences cannot be joined with just a comma (comma splice) or with no punctuation at all (run-on). This is one of the most common errors in TOEFL writing.
"I agree with Claire, she makes a good point."
"Volunteering is important it teaches responsibility."
"I agree with Claire; she makes a good point."
"Volunteering is important because it teaches responsibility."
Fix It With:
- • Period: Make two separate sentences
- • Semicolon: Use ; between related sentences
- • Conjunction: Add and, but, so, because, although
Verb Tense Inconsistency
Mixing tenses within a sentence or paragraph confuses readers. Keep your tense consistent unless you're deliberately showing a time shift.
"I submitted my poems yesterday, and I am wondering if they are received."
"I submitted my poems yesterday and am wondering if they were received."
TOEFL Writing Tense Guide:
- • Email task: Usually present tense for current issues, past for describing events
- • Discussion task: Present tense for opinions, past for examples
- • Build a Sentence: Match the tense established in the context sentence
Article Mistakes (a/an/the)
Articles are difficult for many English learners. Missing articles or using the wrong one affects fluency and can confuse meaning.
"I had a problem with the online form." (first mention)
"Volunteering is a important activity."
"I had a problem with an online form." (first mention)
"Volunteering is an important activity."
Article Rules:
- • a/an: First mention of a non-specific noun; "an" before vowel sounds
- • the: Specific item both writer and reader know about
- • No article: General statements about plural or uncountable nouns
Unclear Pronoun Reference
Pronouns (he, she, it, they, this, that) must clearly refer to a specific noun. Vague references confuse the reader.
"Andrew said students need free time. This is why I disagree."
"When Claire talked to Andrew, she mentioned her concern." (whose concern?)
"Andrew said students need free time. This argument is why I disagree."
"When Claire talked to Andrew, Claire mentioned her concern."
Clarity Check:
- • After writing "this" or "that," add a noun: "this idea," "that concern"
- • If two people could be "she" or "he," use the actual name
- • "It" should have a clear antecedent in the same or previous sentence
Word Order Mistakes
Critical for Build a Sentence! English has strict word order rules that differ from many other languages. Getting word order wrong costs you the entire point on Build a Sentence items.
"The old city tour guides were fantastic."
"I very much like your magazine."
"Always students need support."
"The tour guides in the old city were fantastic."
"I like your magazine very much."
"Students always need support."
English Word Order Essentials:
- • Basic: Subject + Verb + Object (SVO)
- • Adverbs of frequency (always, often, never): Before the main verb, after "be"
- • Adjectives: Before the noun they modify
- • "Very much": After the verb, not before
Mastering grammar rules takes consistent practice and review
Preposition Errors
Prepositions (in, on, at, for, to, with) are notoriously difficult because they don't follow consistent logical rules. Many are idiomatic and must be memorized.
"I had a problem in the submission form."
"I agree to Claire."
"I'm interested for volunteering."
"I had a problem with the submission form."
"I agree with Claire."
"I'm interested in volunteering."
Common TOEFL Preposition Combos:
- • agree with (a person/idea) | agree to (a plan/request)
- • interested in | excited about | worried about
- • problem with | solution to | reason for
- • depend on | focus on | rely on
Sentence Fragments
A sentence must have a subject and a verb and express a complete thought. Fragments are incomplete sentences that can't stand alone.
"Students who work part-time."
"Because volunteering teaches empathy."
"For example, helping at a food bank."
"Students who work part-time have limited free time."
"Volunteering is valuable because it teaches empathy."
"For example, helping at a food bank is rewarding."
Fragment Check:
- • Does it have a subject? (who or what is doing the action)
- • Does it have a main verb? (not just -ing words alone)
- • Does it express a complete thought? (not just a dependent clause)
Parallel Structure Errors
When listing items or comparing things, keep the grammatical structure consistent. This creates smooth, professional writing.
"Volunteering teaches empathy, responsibility, and how to work with others."
"I like to read, writing, and to practice."
"Volunteering teaches empathy, responsibility, and teamwork."
"I like reading, writing, and practicing."
Parallel Structure Rules:
- • Lists: Use same word form (all nouns, all verbs, all -ing forms)
- • Comparisons: Match structure on both sides of "than" or "as"
- • Pairs (both...and, either...or): Keep structures matching
Misplaced Modifiers
Modifiers (adjectives, adverbs, phrases) should be placed next to the word they modify. Misplaced modifiers create confusing or unintentionally funny sentences.
"Walking to school, the rain started falling."
"I only want to help on weekends."
"While I was walking to school, the rain started falling."
"I want to help only on weekends."
Modifier Placement Tips:
- • Place modifiers as close as possible to the word they describe
- • "Only," "just," "even" should go directly before what they modify
- • Opening phrases must relate to the subject of the main clause
Quick Reference: All 10 Mistakes
Subject-Verb Agreement
Match subject & verb number
Run-on Sentences
Use periods, semicolons, or conjunctions
Verb Tense
Keep tense consistent
Articles
Learn a/an/the rules
Pronoun Reference
Make references clear
Word Order
Follow SVO pattern
Prepositions
Memorize common combinations
Fragments
Ensure complete thoughts
Parallel Structure
Match list formats
Modifiers
Place next to what they modify
Visual Summary: Common Grammar Mistakes at a Glance
Save or bookmark this infographic for quick reference when practicing. It summarizes all 10 common grammar mistakes and how to avoid them.
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Try Grammar CheckReferences & Further Reading
- TOEFL iBT Writing Section — ETS Official Website (Accessed: December 2025)
- TOEFL iBT Test Preparation Resources — ETS TOEFL Preparation (Accessed: December 2025)
- TOEFL iBT Writing Scoring Guides — ETS Scoring Rubrics (Accessed: December 2025)
- Common Grammar Errors in Academic Writing — Purdue Online Writing Lab (OWL) (Accessed: December 2025)
- Subject-Verb Agreement Rules — Purdue Online Writing Lab (OWL) (Accessed: December 2025)
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