The Missing /s/: Why a Tiny Sound Costs Big Marks

Yesterday in my KET review class, I corrected one of my 12-year-old Vietnamese students.

Zac: "I go there when my brother birthday and my mother friend birthday."
Me: "My brother's birthday? My mother's friends? Zac, please say the words again."
Zac: "Do I have to pronounce it?"

This is not laziness. This is a systematic pattern documented in research on Vietnamese English.

Why Vietnamese Learners Drop the Final /s/
Research shows that Southeast Asian learners, including Vietnamese learners, frequently omit word-final consonants in English speech (Disney & Le, 2024). Vietnamese phonology does not permit final consonant clusters and allows only a limited set of single final consonants, often unreleased, which makes English final clusters highly marked for these learners (as cited in Phí, 2025).

An error analysis reveals that Vietnamese learners often omit /s/ and /z/ in final positions (Ha, 2005, as cited in Dao, 2018). Schuberg et al. found that when Vietnamese learners read passages, the most common error was neglecting to pronounce a final consonant at all.

A recent large-scale study using authentic spoken data from 16 Vietnamese adult learners found an overall omission rate of 28.4% of expected /s/ and /z/ instances. Crucially, morphological {-s} when preceded by a consonant has the highest error rate at 50.7% (Disney & Le, 2024). That is exactly what happens in "mother's friends" - two consonants before the /s/.

The 3 Jobs of Final /s/ in English
As I discussed in my previous post on why Vietnamese learners drop final /s/ (Tordecillas, 2026), we often think final sounds are just "accent." But in English, final /s/ carries grammar.

1. The /s/ for Plural = How Many?
For example, "one book vs. two books" – the /s/ tells us if it's one or more than one. Research shows students are more likely to drop this kind of /s/ — the grammar /s/ — than the /s/ that is part of the word itself (Disney & Le, 2024). So when a student says "I have two brother," the examiner does not think it's a pronunciation problem. The examiner thinks it's a grammar mistake. Why? Because in English, the last sound of the word is often what gives us the meaning. If we don't hear that last sound, we lose the meaning (Phí, 2025).

2. The /s/ of Possessive = Whose?
For example, "my mother friend vs. my mother's friend" – without the /s/, the possessive relationship disappears. For KET, this is tested directly in possessive 's.

3. The /s/ of Present Simple = Who Does It?
For example, "I go vs. He goes" – when students drop this /s/, they lose the most marks. The Cambridge KET assessment criteria penalize errors in "simple grammatical forms." "My brother go" is marked as a grammar error, not pronunciation.

What's the Impact on KET / PET / IELTS Scores?
KET (A2) & PET (B1): Cambridge speaking is marked for Grammar & Vocabulary together. Slobin (1992) points out that in L2 acquisition, speakers delete surface forms, and examiners interpret this as lack of grammatical control. A student who consistently says "brother birthday," "two book," "he go" will be placed in Band 2-3 out of 5 for Grammar and Vocabulary. Students often replace English ending sounds with sounds common to both languages (Tang, 2007, as cited in Nguyen & Dang, 2022).

IELTS: For Pronunciation Band 5, frequent lapses in features like final /s/ cause breakdowns. For Grammar, omission of plural and third-person -s is a persistent Band 5 feature.

How I Explained It (In English, On the Board)

I typed his sentence:

I go there when my brother birthday

Then I added the /s/ visually:

my brother + 's = my brother's = birthday OF my brother

my mother + 's + s = mother's friends = MANY friends BELONGING TO mother

I said: "Look Zac, without /s/, I don't know WHO or HOW MANY. If you don't pronounce the final /s/, the examiner thinks you don't know grammar."

He responded: "Oh..."

--- References

Dao, D. N. A. (2018). Learners' perspectives on English pronunciation teaching and learning: A preliminary study in the Vietnamese context. In Proceedings of the 9th Pronunciation in Second Language Learning and Teaching conference (pp. 86–99).

Disney, S. J., & Le, L. N. C. (2024). Word-final /s/-/z/ omission in Vietnamese English. Languages, 9(10), 327. https://doi.org/10.3390/languages9100327

Ha, C. T. (2005). Common pronunciation problems of Vietnamese learners of English. Journal of Science, Foreign Languages, Hanoi National University.

Nguyen, N. H. T., & Dang, N. V. B. (2022). Common mistakes in English speaking affected by Vietnamese of Master of Business Administration at Tay Do University. International Journal of Social Science and Human Research, 5(5), 1791–1808.

Phí, T. T. T. (2025). Problems in the pronunciation of English consonant clusters – A case study of English-majored students at a Vietnamese university. International Journal of Social Science and Human Research, 8(9).

Slobin, D. I. (1992). The crosslinguistic study of language acquisition. Lawrence Erlbaum.

Tordecillas, J. (2026, September 11). Why Vietnamese learners drop final /s/. https://jemtordecillas.blogspot.com/2026/09/why-vietnamese-learners-drop-final-s.html

Read Part 1: Why Vietnamese Learners Drop Final /s/ - The Pronunciation Roots

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