The emphasis of learning to learn in curriculum reform has signaled to teachers to adopt student-centered strategies of teaching and different modes of assessment. Cooperative learning, as an innovative instructional strategy, and portfolio assessment, as an alternative assessment, are increasingly being used in Hong Kong classrooms. The change from listening to teachers teach and answering examination questions to taking the initiative to learn and demonstrating competence with self-selected evidence is a great challenge to the students. This paper first discusses the various constraints and difficulties of using cooperative learning and portfolio assessment that Hong Kong teachers and students are encountering, such as the large class size, using social skills in group discussion, writing reflective statements, choosing evidence for inclusion in portfolios, grading portfolios and conducting self and peer assessment. Then examples are drawn from schools of small classes to investigate how the teachers attempt to tackle the problems and difficulties in implementing cooperative learning and portfolio assessment in their schools. The paper concludes with a discussion of the implications for successful use of portfolio assessment.