The current study examined the effects of socioeconomic status (SES) on the school readiness of Chinese preschool children in Hong Kong. A total of 69 teachers from 20 kindergartens in both rich and poor districts in Hong Kong rated the school readiness of 567 preschool children using the Chinese version of the Early Development Instrument. Information about home learning activities and kindergarten characteristics was obtained from parents and preschool teachers, respectively. The results indicated a gradient relationship between SES and total EDI scores, with children from higher-SES families rated as being very ready for school on more domains of the Chinese version of the Early Development Instrument than those from lower-SES families. Home learning activities (reading and recreational activities) and teachers’ experience and kindergarten facilities significantly mediated the socioeconomic gradient effects. These findings highlight that efforts are much needed in tackling the developmental disparity and the promotion of better parent–child interaction, teacher quality, and kindergarten facilities might be able to help all children attain their own developmental potential.