We examine the effects of family structures and processes on student achievement in Hong Kong. Specifically, we show that the negative effects of single parenthood in past studies are not universal. In Hong Kong, 4,405 15-year-old students completed a questionnaire, and tests in reading, mathematics and science. We analysed the data using multilevel models of Rasch test scores and Warm estimated indices of questionnaire items. In all subjects, the scores of children living with single parents did not differ significantly from those of children living with two parents. Moreover, students living with no parents had lower reading and science scores than other students, and this effect was mediated by lower family investment and involvement. (Contains 1 table and 1 note.)