The study draws upon a conceptual framework of the three assessment approaches (assessment of/for/as learning) and a five-phase cycle of bilingual classroom assessment that subsumes (1) planning assessment, (2) collecting and organizing assessment information, (3) interpreting assessment information and providing feedback, (4) evaluating and reporting assessment information, and (5) taking action on the assessment results. Within this framework, the purpose of the study is to develop five modules of bilingual classroom assessment across the bilingual curricular on the arts, the health and physical education areas, cross-area project, and the using English as a medium of instruction in the English subject (i.e., the EMI). By the design-based research approach, the study investigated how the bilingual classroom assessment practices were contextualized and developed with foci on the lesson planning, the instruction implementation, and post-lesson reflections from the teachers’ perspectives. Data-collection techniques included via interviews, lesson co-planning notes, lesson observation notes, students’ worksheets and assessments, and the teachers’ post-lesson reflections. Five secondary schools (4 junior high schools, 1 senior high school) and 7 teachers (3 English teachers, and 4 content area teachers) partook in the study. Preliminary findings revealed the five assessment modules that detail why, what, how, and so what of the assessment, alongside a succinct lesson plan of a unit (a range of 3 to 16 class periods). In terms of post-lesson reflections, content-area teachers emphasized the importance of aligning classroom participation and English learning targets with the assessment tasks, so as to facilitate the dual-focused learning of Grades 7 and 8 students in bilingual classrooms. In terms of EMI, English-subject teachers indicated a need to set fewer learning targets as well as to slower the instructional pacing, so as to guide the self-directed English learning of Grade 7 students. The study delineates the implications of bilingual classroom assessment.