This study investigates 201 Singaporean teachers' perceptions of their technological pedagogical content knowledge (TPACK), lesson design practices, and design dispositions through a survey instrument. Investigation of these constructs reveal important variables influencing teachers' perceptions of TPACK which have not yet been explored. The confirmatory factor analysis and reliability analysis confirm the validity and reliability of the instrument. The structural equation model shows that the teachers' perceptions of design dispositions (orientations towards design) and lesson design practices (approaches used for lesson design) have direct relationships with the teachers' perceptions of TPACK. The results of this study show that to enhance teachers' TPACK perceptions, teacher educators need to help teachers develop lesson design practices that support ideation and iteration. They also need to develop teachers' design dispositions that are amenable to exploring and resolving conflicting lesson design ideas. Going beyond TPACK, understandings of teachers' lesson design practices and design dispositions are important for teacher educators to better design professional development for integration of information and communications technology.