This study assessed the effect of a teacher professional development (PD) programme that incorporated culturally responsive teaching on Chinese kindergarten teachers' perceptions of learning motivation of ethnic minority (EM) vs. Chinese pupils in Hong Kong. The moderating role of classroom ethnic composition was examined. Forty-five teachers in the intervention group attended 20 sessions of PD courses over 10 months, whereas 40 teachers who did not attend the current programme formed a control group. Pre- and post-tests were conducted to assess teacher perceptions of learning motivation and engagement of Chinese and EM pupils. Hierarchical structure of data was accounted for with multilevel modelling. Results showed that the intervention resulted in positive changes in teacher perceptions of learning motivation of EM (vs. Chinese) pupils among teachers working in classrooms with low proportions of EM pupils when compared to teachers in the control group. The findings highlighted that teachers' cultural diversity training programmes should be evaluated in relation to classroom ethnic composition and other contextual factors that influence the quality and frequency of interethnic contact.