While teacher assessment and student engagement are emerging topics in the field of second language (L2) writing, little is known about the possible correlations between the two important constructs. This mixed-methods study first surveyed the perceived teacher assessment approaches among L2 learners whose majors are English, Japanese and French in Chinese universities, and then explored their engagement in L2 writing. Follow-up interviews were conducted with individual students for triangulation of the survey results. The quantitative results showed that formative and portfolio writing assessments positively predicted students' planning, task management and persistence in L2 writing, whereas summative writing assessment negatively predicted their persistence. The findings showed that the formative assessment approach predicted the use of planning only for French majors, task management for French and Japanese majors, and persistence only for French majors. The portfolio assessment approach predicted planning for Japanese majors and persistence for English majors. The qualitative findings supported the quantitative results and revealed that English learners were different from the Japanese and French learners in terms of prior language learning and assessment experiences. Pedagogical implications are discussed.