The Council for the Accreditation of Educator Preparation (CAEP) Standards requires educator preparation programs (EPPs) to ensure instruments used to assess their candidates are both valid and reliable. Due to size and limited financial resources, this task may be challenging for some EPPs. In an effort to address CAEP's expectations, 26 EPPs in one state formed a collaboration to develop and implement an instrument for use during student teaching, and then conducted analyses of its data to determine the validity and reliability. This article uses a case study methodology to investigate the EPPs' motivations for participating in the collaboration, and the benefits, challenges, and learning that resulted from participation. The findings, principally related to aspects of individual program improvement, have implications not only for EPPs pursuing CAEP accreditation but also for any higher education institutions interested in collaborative assessment development.