The purpose of this study was to adapt Teachers' Conceptions and Practices of Formative Assessment Scale (TCPFS) based on the Theory of Planned Behavior (TPB) into Turkish culture and apply the TPB to examine teachers' intentions and behaviors regarding formative assessment. After examining linguistic validity of the scale, Turkish scale was applied to 400 primary school teachers in Turkey. Confirmatory factor analysis (CFA) was administered for the construct validity. The results showed that the model had fairly good model fit (RMSEA = 0.07, CFI = 0.90, TLI = 0.87, IFI = 0.90). Reliability of the Turkish version of the scale was attained through Cronbach's alpha coefficient. Findings revealed that adapted scale has satisfactory psychometric features. Since the psychometric properties of the scale in the TPB were acceptable, predictive model was estimated. Structural equation modeling was used to examine the applicability of TPB in understanding teachers' conceptions and practices of formative assessment. The results supported that TPB model can help to predict and explain teachers' conceptions and behaviors regarding formative assessment.