This study examines how the language used at home, Putonghua or Cantonese, has influenced the Chinese reading attainment of 4335 primary school students in Hong Kong. Also examined was the influence of the birthplace and home background socioeconomic status (SES) of the reader. Although the indigenous Hong Kong population uses Cantonese, a dialect of Chinese, for everyday communications, the Chinese written in school is Modern Standard Written Chinese (MSWC), the written equivalent of Putonghua, the spoken language of the people of China. Many of the numerous families migrating from China to Hong Kong in recent years have brought with them children educated in Putonghua in China and with extensive experience of MSWC. It was hypothesised that the reading attainment of these students would be superior to that of classmates born in Hong Kong and using Cantonese habitually. This would apply particularly to students from advantaged SES homes. The children born in China indeed had superior reading attainment. But children speaking Cantonese at home and Putonghua 'sometimes' had the highest reading scores, regardless of their birthplace or SES. The writers reflect on assumptions about the influence of the language used at home on language attainment and the implications for educational planning. [Copyright of Journal of Multilingual and Multicultural Development is the property of Routledge. Full article may be available at the publisher's website: http://dx.doi.org/10.2167/jmmd529.1 ]