Over the last decade, teacher performance assessments (TPAs) have begun to find appeal in the context of teacher education programs and teacher licensing for their innovative ways of assessing teacher knowledge and skills but primarily for their potential to promote teacher learning and reflective teaching. Studies of preservice teachers who have completed a TPA, portfolio assessments in particular, have examined learning outcomes for teachers and have generally found positive effects on their learning. In 1998, the state of California passed legislation (SB2042) that would require teacher candidates enrolled in credential programs to successfully complete a teaching performance assessment to obtain a preliminary teaching credential. Programs had two options: they could administer the TPA designed by the state in consultation with the Education Testing Service (ETS), or develop their own TPAs, provided they met the state's Assessment Quality Standards. This study was conducted as part of an investigation of the Performance Assessment for California Teachers (PACT), an alternative performance assessment designed and piloted in the spring of 2003 by a consortium of preservice teacher preparation programs throughout the state (all of which are post-baccalaureate programs with lengths ranging from two semesters to two years). Understanding that high-stakes assessments ultimately drive instruction and learning, these programs opted to create and pilot their own performance assessment that was designed to be an authentic representation of teaching and to also reflect their program values and goals. This article provided a timely opportunity to examine the impact of a performance assessment on preservice teacher learning and teaching practice as well as the assessment's contribution to teacher education programs. Drawing on case studies of two teacher candidates who participated in the first year (2002-03) pilot of the PACT at one campus, this study disentangles what teacher candidates reported learning from completing the elementary teaching event from other sources of learning in their credential program, examines the way the learning and teaching contexts in which teacher candidates completed the assessment affected their learning experiences, and corroborates teacher self-report with observational data and evidence from lesson debriefs. A focus group and data from two surveys provide for greater generalizability of the findings and a comparison of the experiences of teacher candidates at one campus to those of candidates across campuses. (Contains 2 tables and 6 notes.)