This action study embraces Stassen’s four principles for good practice in assessment in higher education by involving candidates of two programs—a teacher preparation program and an administrator preparation program—collaborating on an assessment project. Preservice teachers submitted “authentic” artifacts from their student-teaching experience (e.g., a videotaped lesson), while aspiring school leaders provided a detailed analysis using an assessment rubric. Results and lessons learned from this type of collaborative assessment are shared. The authors conclude by offering a model regarding how the four principles of best practice can be embedded in an assessment project that facilitates student learning.