This study explores how the concept of Assessment for Learning (AfL) is practised in the CLIL contexts. It focuses on the assessment purpose of understanding and supporting students' content and language learning. Ten CLIL teachers in the bilingual program of three different regions in Taiwan were involved in the study. Results from the class observations and semi-structured interviews indicated that four formative assessment approaches -- questioning techniques, worksheets, peer and self-assessment, and formative use of summative tests -- were frequently carried out in CLIL classes. A synergy of assessment tools was also found in the observed CLIL class, which provides students, teachers, and parents with a continuing stream of evidence of student progress and skill. Findings showed that the teachers were aware of AfL and promoted it through various formative assessment practices in their CLIL classes. This study provides insights into the development of alternative instruments that can be used to assess EFL more comprehensively in the CLIL classroom context of elementary education.