The 12 Most Common Grammar Mistakes ELL Students Make (and How to Actually Fix Them)

If you've ever read 30 ELL essays in one sitting, you know the truth: the same 10–12 grammar errors appear over and over, across grade levels, across L1s, across years in the U.S.

That's actually good news. It means you don't need to teach 'all of English grammar.' You need to teach the predictable errors well.

This post catalogs the 12 most common grammar mistakes I've seen in 10+ years of secondary ELL writing, ranked roughly by frequency. For each one: what causes it, who's most likely to make it, and what actually fixes it — not just what looks good on a worksheet.

Pair this with our Ultimate Guide to Teaching Grammar to ELL Students and the Grammar Intervention Strategies toolkit.

1. Missing or Wrong Verb Tense

Looks like: Yesterday I go to the store.

Why it happens: Chinese, Vietnamese, and Korean don't inflect verbs for tense — they use time words. Students transfer that strategy to English.

The fix that works: Teach the sound of -ed (see How to Teach Verb Tenses to ELLs), then drill switching between simple present and simple past in dictation. Tense flexibility, not isolated forms.

2. Subject-Verb Agreement (Third-Person -s)

Looks like: She walk to school every day.

Why it happens: Third-person -s is one of the last morphemes acquired (Krashen's morpheme order studies, 1977 and replicated since). It's also semantically empty — dropping it doesn't lose meaning, so the brain ignores it.

The fix that works: Don't drill it as a rule. Build a minimal pair habit: every time students hear he/she/it, they listen for the -s. Color-code subjects in mentor sentences. See Subject-Verb Agreement Drills.

3. Article Confusion (a / an / the / Ø)

Looks like: I went to store and bought the milk.

Why it happens: Most of the world's languages don't have articles. Russian, Mandarin, Korean, Japanese, Polish, Vietnamese — no articles at all. Spanish and Arabic do have articles but use them differently than English.

The fix that works: Stop teaching the rules ('use the for specific things'). Teach the flowchart: Is it countable? Singular or plural? First time mentioning it? Specific or general? See our deep dive on teaching articles to ELLs for the printable decision tree.

4. Prepositions

Looks like: I'm good in math. On Saturday in the morning at 8 o'clock.

Why it happens: Prepositions are largely arbitrary. They don't translate one-to-one between languages. There's no rule that explains in love, on time, at home.

The fix that works: Teach prepositions in chunks, not in isolation. Depend on, interested in, good at — these are vocabulary items, not grammar rules. Build a class anchor chart and add to it weekly.

5. Word Order in Questions

Looks like: Where you are going? What time the bus comes?

Why it happens: English requires subject-auxiliary inversion in questions, which is unusual cross-linguistically. Spanish, French, and most Asian languages don't invert this way.

The fix that works: Drill the Question Word + Auxiliary + Subject + Verb pattern with color blocks. Then practice in pairs — every student asks 5 information questions per class for a week.

6. Plural -s (Inconsistent Use)

Looks like: I have three book.

Why it happens: Many L1s mark plurality with separate words or context, not endings. Plus, English has irregular plurals (children, feet, mice) that contradict the rule students just learned.

The fix that works: Pair plural drilling with quantifiers — three books, many books, a few books. Quantifiers cue the plural and reinforce the morpheme.

7. Pronoun Confusion (he/she Mix-Ups)

Looks like: My mom said he will come.

Why it happens: Many languages (Turkish, Persian, Hungarian, spoken Finnish) have one gender-neutral third-person pronoun. Students transfer that single form to English and use he or she interchangeably.

The fix that works: Don't shame the error — name the cause. Then drill with photo cards: students describe people aloud, forcing the pronoun choice. Make it a low-stakes routine, not a high-stakes correction.

8. Run-On Sentences and Comma Splices

Looks like: I went to the store, I bought milk, my mom was happy.

Why it happens: Many writing traditions value long, flowing sentences. Punctuation conventions vary widely. Students aren't being lazy — they're applying a different rhetorical norm.

The fix that works: Teach the three repairs: period, semicolon, or coordinating conjunction (FANBOYS). Practice on student writing, not contrived examples. See Sentence Structure Activities.

9. Fragments

Looks like: Because I was tired. Even though we tried hard.

Why it happens: Subordinating conjunctions are tricky — they sound complete in speech (we use them all the time as standalone replies). The written rule that they must attach to an independent clause feels arbitrary.

The fix that works: The finish-the-sentence drill. Give students 10 dependent clauses; they complete each one with an independent clause. Builds the syntactic intuition fast.

10. Wrong Word Form (Noun vs. Verb vs. Adjective)

Looks like: The book was very interest. I want to success.

Why it happens: English derivational morphology is dense. Interest, interested, interesting, interestingly — four forms of the same root. Students learn one and stretch it to fit all contexts.

The fix that works: Teach word families explicitly. Build a 4-column chart (noun / verb / adjective / adverb) every time you encounter a new academic word. The Academic Word List (Coxhead, 2000) gives you the highest-leverage 570 word families to focus on.

11. Missing or Incorrect Be Verb

Looks like: She tired. They at school. He is go to the gym.

Why it happens: Russian, Arabic, Hebrew, and Mandarin drop the copula (be) in present tense. Students transfer that pattern, then over-correct by inserting be where it doesn't belong.

The fix that works: A 2-minute daily routine: photo of a person, students produce three be sentences (She is happy. She is at the park. She is wearing a hat.). Routine builds automaticity.

12. Direct Translation Idioms

Looks like: I have 15 years. (Spanish tener años) Make a photo. (German/Russian machen ein Foto)

Why it happens: Idioms and collocations don't transfer. The L1 collocation feels natural, so the student translates it word-for-word.

The fix that works: Build a class 'False Friends' wall. Every time an idiom appears, post the L1 version next to the English version. Awareness drops the error rate dramatically.

What the Research Says About Error Correction

Two findings from the last 20 years that should shape your practice:

First, John Truscott's controversial 1996 paper The Case Against Grammar Correction in L2 Writing Classes argued that error correction doesn't work. The research since (especially Bitchener and Ferris) has nuanced this: comprehensive correction doesn't work, but focused correction on a single recurring error does.

Second, Lyster and Ranta's 1997 study on corrective feedback in immersion classrooms found that recasts (just restating the correct form) had the lowest uptake. Elicitation and clarification requests — asking students to self-correct — had the highest. In other words, don't fix it for them. Make them notice it.

Practical translation: when you see one of these 12 errors in writing, underline it and write the error type in the margin (e.g., 'verb tense'). Don't write the correction. Make the student do the cognitive work.

Frequently Asked Questions

Should I correct every error in student writing? No. Pick one error type per assignment and mark only that. Students learn more from depth than from breadth of correction.

My students keep making the same error after I correct it. Why? Either the structure isn't developmentally ready (see Pienemann), or you're correcting without forcing self-correction. Try elicitation instead of recasts.

How do I track which errors each student makes? Keep a class error log — a Google Sheet with student names down the side and the 12 errors across the top. Two minutes per essay to tally. After 4 weeks you know exactly what to teach.

Are some of these errors more important than others? Yes. Verb tense, subject-verb agreement, and run-ons affect comprehension. Article errors and pronoun confusion rarely do. Prioritize the ones that obscure meaning.

Do these errors appear in all ELLs equally? No — L1 strongly predicts which errors you'll see. Use the L1 notes above to anticipate.

Where to Go Next

Three concrete next steps:

1. Pick one error. Choose the most common one in your class and design a 2-week mini-unit around it.
2. Download the diagnostic. Our Common Errors Detective Sheet walks students through self-editing for all 12 errors.
3. Automate the practice. Grammar Spy Membership targets each of these 12 errors with adaptive missions that adjust to the specific errors your students keep making.

Teach the predictable errors well. Skip the unpredictable ones until they appear in writing. That's the whole job.