Children have formal science instruction from kindergarten in Australia and from Year 3 in China. The purpose of this research was to explore the impact that different approaches to primary science curricula in China and Australia have on children's conceptual understanding of science. Participants were Year 3 children from three schools of high, medium and low socio-economic status in Hunan Province, central south China (n = 135) and three schools of similar socio-economic status in Western Australia (n = 120). The students' understanding was assessed by a science quiz, developed from past Trends in Mathematics and Science Study science released items for primary children. In-depth interviews were carried out to further explore children's conceptual understanding of living things, the Earth and floating and sinking. The results revealed that Year 3 children from schools of similar socio-economic status in the two countries had similar conceptual understandings of life science, earth science and physical science. Further, in both countries, the higher the socio-economic status of the school, the better the students performed on the science quiz and in interviews. Some idiosyncratic strengths and weaknesses were observed, for example, Chinese Year 3 children showed relative strength in classification of living things, and Australian Year 3 children demonstrated better understanding of floating and sinking, but children in both countries were weak in applying and reasoning with complex concepts in the domain of earth science. The results raise questions about the value of providing a science curriculum in early childhood if it does not make any difference to students' conceptual understanding of science. (Contains 5 tables and 2 figures.)