This study examines teachers' intention to engage in School Based Assessment (SBA) in secondary schools of Sri Lanka, by utilising Ajzen's (1985) Theory of Planned Behaviour. Multiple regression analysis was employed for data analysis. Given the recent attention on curricular reforms in many countries, this study contributes to the limited research on SBA from a developing country perspective and provides better understanding of factors that motivate teachers to engage in SBA. The findings of the study indicate that teachers' subjective norm and perceived behavioural control are significant predictors of their intention to engage in SBA, not their attitudes. This study also emphasises the need for policy makers to devise more effective strategies to design programs to encourage teachers to engage in SBA.