Past studies identified isolated factors influencing teachers' formative assessment practices (FAP) but did not show a comprehensive model of it. Hence, this study systematically creates and tests a theoretical model of FAP by determining whether personal or contextual factors are linked to teachers' FAP. We collected longitudinal data from 296 Hong Kong primary and secondary teachers through two waves of the survey. The results of a multivariate outcome, multilevel analysis showed that personal (teacher rank, years of teaching experience, and self-efficacy) and contextual factors (school support, total number of teachers in a school, and teaching grade) significantly impact teachers’ FAP. Copyright © 2022 The Authors. Published by Elsevier Ltd.