Vietnamese and English organise sound very differently, which means Vietnamese-speaking children hit a specific, predictable set of trouble spots in English phonics — not random difficulty, but patterns you can target directly.
Trouble spot 1: consonant blends and clusters
Vietnamese syllables are generally simpler than English ones and don't stack consonants together the way English does at the start or end of a syllable — there's nothing in Vietnamese quite like the bl in blue or the -sts ending in tests. This makes English consonant blends a genuinely harder skill, not a minor detail — extra, deliberate practice on our consonant blends list is worth prioritising.
Trouble spot 2: the "th" sounds
Neither the voiceless th in think nor the voiced th in this exists in Vietnamese, so these two sounds need to be explicitly modelled and practised rather than assumed — our digraphs guide covers both directly.
Trouble spot 3: dropped final consonants
Vietnamese speech often doesn't fully release the final consonant of a syllable, so when reading English aloud, endings can get quietly dropped — this shows up especially in the plural -s and past tense -ed, which change a word's grammar and meaning in English in a way that's easy to miss if the ending isn't clearly pronounced. Deliberate, slightly exaggerated final-sound practice helps this stick.
Tone vs stress: a different kind of adjustment
Vietnamese is a tonal language, where pitch changes a word's meaning. English doesn't use tone this way, but it does use word stress (which syllable gets emphasis) in ways that affect meaning and rhythm. This is more about explicit attention to stress patterns than a sound-level phonics fix, but it's worth knowing about as a related adjustment.
For the broader picture of teaching English phonics to any non-native speaker, see our phonics for ESL kids guide, and for general bilingual development questions, see phonics for bilingual children.