Phonics teaches children how letters match sounds. For example, c-a-t makes 'cat'. English spelling is not easy. The letter 'a' sounds different in 'cat' and 'cake'.

A study of 38 experiments found that phonics helps children in English-speaking countries start reading. But for children who learn English as a foreign language, phonics helps them hear sounds, but it may not help them understand stories.

English spelling is complicated. The letter 'a' sounds different in 'cat', 'cake' and 'father'. Phonics teaches the rules that connect letters and sounds step by step. In 2001, Ehri and colleagues reviewed 38 experiments for the US National Reading Panel. They found that systematic phonics had a moderate effect, and the effect was larger when children started early.

However, a 2017 review of 15 studies of children learning English as a foreign language found that phonics improved sound skills, but its effects on reading real words quickly and on reading comprehension varied. One possible reason is that these children often do not know the meanings of the words they can sound out.

English spelling matches sounds far less consistently than Japanese kana does, so systematic phonics, which teaches letter-sound correspondences in a planned sequence, has long been promoted as the way into reading. The strongest evidence comes from a 2001 meta-analysis by Ehri and colleagues for the US National Reading Panel, covering 38 experiments and 66 comparisons. Systematic phonics had a moderate overall effect.

The effect was larger when instruction began early and smaller after first grade, with benefits for word reading, spelling and text comprehension. A 2019 British review of earlier reviews agreed that the evidence favored phonics but judged its quality lower than often assumed. For children learning English as a foreign language, the evidence is thinner still. A 2017 synthesis of 15 studies found consistent gains in phonemic awareness and in decoding made-up words.

Effects on reading real words and on comprehension were inconsistent, and many studies had methodological weaknesses. One likely reason is vocabulary. A native speaker who sounds out a word has usually heard it many times already. A foreign-language learner can often pronounce a word correctly without knowing what it means. For these learners, phonics works best alongside vocabulary building and plenty of listening.