While there is extensive literature on how classroom-based assessment (CBA) can be effectively put into practice, little is known about its implementation in L2 contexts, especially in the young English-as-a-foreign-language (EFL) learner context. This study endeavored to investigate teachers' CBA practices and factors that might exert influences on them. A purposive sample of three EFL teachers from two primary schools participated in this case study. Our thematic analysis revealed that the potential of CBA in supporting young EFL learners' learning had not been fulfilled. The teachers failed to clarify such objectives and success criteria to their students. Despite the use of multiple assessments, the teachers relied heavily on formal assessments, with student-involving assessments being less frequently used. Moreover, there was a heavy reliance on norm-referenced assessment and evaluative feedback. It was also found that teachers' CBA practices faced complex challenges related to teacher, student, context and system factors. Practical implications for how CBA can be effectively implemented in similar EFL contexts are discussed.