The Performance Assessment for California Teachers (PACT) is an authentic tool for evaluating prospective teachers by examining their abilities to plan, teach, assess, and reflect on instruction in actual classroom practice. The PACT seeks both to measure and develop teacher effectiveness, and this study of its predictive and consequential validity provides information on how well it achieves these goals. The research finds that teacher candidates' PACT scores are significant predictors of their later teaching effectiveness as measured by their students' achievement gains in both English language arts and mathematics. Several subscales of the PACT are also influential in predicting later effectiveness: These include planning, assessment, and academic language development in ELA, and assessment and reflection in mathematics. In addition, large majorities of PACT candidates report that they acquired additional knowledge and skills for teaching by virtue of completing the assessment. Candidates' feelings that they learned from the assessment were strongest when they also felt well-supported by their program in learning to teach and in completing the assessment process.