Which English Sounds Are Hardest for Chinese TOEFL Learners?

The data, and one important caveat

Otherwise the method matches the main study: each recording is scored by automatic pronunciation assessment (0–100 per phoneme), and word-final -s is recovered by aligning the target to the recognised words. A sound is ranked within a group only when it accumulates roughly 1,000+ measurements in that group; rarer sounds are left unranked. We report denominators, means, and group differences, but no significance tests — repeated learners and prompts are not independent observations.

Pattern 1: The one sound that actually diverges is /θ/

/θ/ is the hardest sound for the Chinese-interface group at 63.5/100; for the English-interface group it does not rank as a difficulty at all.

The size of the gap is worth pausing on. The Chinese group’s second-hardest sound, /ŋ/ (72.5), already sits about 9 points above /θ/. So /θ/ is not “one more slightly hard sound” — it is a single outlier, cleanly separated from the rest. Of its 3,252 measured occurrences, 36.0% fell below the 60-point threshold.

Pattern 2: Almost everything else is the same

This section is really the control for the last one. If the two groups differ only at /θ/ and match everywhere else, the /θ/ gap is more likely a real linguistic effect than an artefact of sampling or overall level.

Sentence length behaves almost identically too. Reproduction falls as sentences grow in both groups, and the curves nearly overlap — 79.5% vs 81.2% on the shortest sentences, 51.5% vs 53.2% on the longest.

Word-final -s tells the same story: 10.7% dropped in the Chinese-interface group versus 9.6% in the English-interface group. Put together, the picture is clear — the two Listen and Repeat profiles largely overlap, and the one meaningful crack is at /θ/.

How to read this

The largest group — learners who set no interface language — also ranks /θ/ hardest, at about 61, matching the Chinese-interface group. Given LingoLeap’s heavily Chinese-speaking user base, that is consistent with the unset group being largely Chinese-first-language. It corroborates the pattern but is not independent confirmation.

For a Chinese-first-language test-taker, this narrows a vague worry (“my pronunciation isn’t good enough”) into a concrete target: /θ/ is worth isolating and prioritising, while on most other sounds your gap to English-interface learners is small. It also argues for targeting the few sounds that actually diverge by first language, rather than “practising pronunciation” in general.

What this study cannot show

• Interface language is a proxy for, not the same as, first language; it cannot separate heritage speakers, bilinguals, and similar cases.
• Limited coverage: only about 26% of learners set a UI language, and the English-interface group has just 1,045 sessions — a much smaller sample than the Chinese group.
• /θ/ is unranked for the English-interface group because its measurement count fell below the threshold, so we say only that it does not enter the difficulty ranking — not that it is easy for English-interface learners.
• These are automatic-assessment outputs, not phonetician judgements; the /θ/ substitution mechanism (/s/ vs /t/) is not tested directly here.
• The design is observational: no significance tests and no causal claims.

Turn the finding into practice

If you are a Chinese-first-language learner, the most practical next step is to train /θ/ inside real sentences, not in isolation. These two entry points cover the method and the practice:

Dataset note

Notes and sources

1. [1] Best, C. T., & Tyler, M. D. (2007). Nonnative and second-language speech perception. In Language Experience in Second Language Speech Learning (pp. 13–34). John Benjamins.
2. [2] Saito, K. (2019). Effects of second language pronunciation teaching revisited. Language Learning, 69(3), 652–708.
3. [3] Microsoft. (2026). Use pronunciation assessment. Microsoft Learn.

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