The theory of planned behaviour (TPB) was used to explore the Hong Kong teachers' intentions to implement school-based assessment (SBA) and the predictors of those intentions. A total of 280 teachers from Hong Kong secondary schools who had been involved in SBA were surveyed. Rasch-calibrated teacher measures were calculated for each of the 6 variables--affective and instrumental attitude, subjective norm, self-efficacy, knowledge, and intention--regarding SBA. The results of hierarchical multiple regression analysis revealed that instrumental attitude and self-efficacy made significant contributions to predicting intentions to implement SBA. These 2 predictors explained 55.2% of the variance in intentions. The other 3 variables, that is, affective attitude, subject norm, and knowledge, did not have significant predictive power on the formation of intentions to implement SBA. Possible explanations and implications of the findings are discussed.