Assessment is a prominent issue in education today. However, assessment of learning often occurs only at the end of the semester to satisfy accreditation agencies. An alternative is to conduct assessments during the course, not only to assess if learning goals are being met but also to assess student learning during the course. Assessment for learning puts assessment at the heart of the learning process. In this approach, students are active participants in the assessment process. The authors propose a new approach to assessment--group-based assessment (GBA), which includes in-class group learning, peer assessment, and peer and instructor feedback. They develop their approach based on theoretical underpinnings of the dynamic assessment theory and the zone of proximal development theory to develop GBA. The authors test the effectiveness of this approach in a study conducted with students using a one group pretest-posttest quasi-experimental design. The results of this study provide empirical support that GBA is related to students' intrinsic motivation, self-regulated learning strategies, perceived autonomy, perceived competence, task mastery orientation, and actual performance. In addition, guidelines for implementing GBA are provided. (Contains 1 figure and 4 tables.)