As English has increasingly become associated with social and economic power in the context of globalisation, there has been a growing concern regarding achievement gaps in English that appear to be correlated to learners' socio-economic status (SES). The present study aims to examine how parents' SES and their behaviours and beliefs about English education relate to their children's English language learning, and how such relationships may differ across different grade levels. The participants were fourth-, sixth- and eighth-grade students who had learned English from the third-grade level (572 students in total) together with their parents in a medium-sized city in China. An extensive parental survey revealed that while parental beliefs about English education and their beliefs about their children's success in acquiring English did not differ between different SES groups, their direct behaviours (such as providing direct assistance for their children to learn English) and their indirect behaviours (such as the home literacy environment and indirect modelling they provided) showed significant differences by the fourth-grade level. Combined with the students' learning outcome data, it was found that while the parents' SES did not show much effect on their children's listening and reading/writing performance during their elementary school years, it did indicate an effect on their speaking abilities at the fourth-grade level, if not earlier. This paper suggests the importance of incorporating socio-economic dimensions in theorising second and foreign language acquisition (SLA), which are largely missing in current major approaches in SLA.