It is not known whether children who are struggling with reading in a non-dominant language will respond better to a phonological intervention or to one that addresses oral proficiency. Multilingual seven-to nine-year-olds showing reading difficulty in a non-dominant language, English, were given a three-week intervention in phonological skills or in language proficiency and were compared with two control groups (one with reading difficulties and one with no reading difficulties) who received a non-language based intervention. The group receiving the explicit phonological instructions showed significantly better gain in reading and spelling measures than the language proficiency and reading difficulties control group, but did not reach the levels of the noreading-difficulty group. The phonological intervention was particularly effective for children with the lowest single-word reading scores. We suggest that the intervention helped to catalyse the fine-tuning of the phonological domain, making phonological representations optimally available for decoding, phonological manipulations and literacy development.