Learning to teach is a complex and multidimensional process. Many teacher educators agree that learning to teach occurs when theory connects with practice, general propositions and abstract concepts are instantiated in clinical contexts, and field experiences are interpreted in light of a coherent knowledge base. The recently redesigned curriculum of STEP is based on the assumptions that learning to teach requires a tightly-coupled and consistent curriculum with two interlinked strands--one university-based, the other school-based. Furthermore, the process of learning to teach requires planning and trying out plans, thinking and testing ideas, acting and evaluating the consequences of one's actions, discussing and assessing one's work in the company of mentors and colleagues. The current design of the STEP curriculum seeks to integrate many areas of knowledge that underlie effective teaching. Within this curriculum, teacher candidates observe, plan, practice, and assess pedagogical approaches in specific clinical contexts. To focus on important aspects of teaching and to develop professional consensus among members of the STEP community, one of the central elements of the redesign effort was the incorporation of professional standards in the assessment of teacher candidates' growth and development in their clinical practice as well as in their coursework. This standards-based approach to systematic assessment replaced a process of open-ended observations and subjective assessments of the candidates' performances in their field placements that varied greatly based on the views and observation capacities of different users. In this study, the authors analyze these assessments of the student teachers' clinical performances for the STEP class of 1999/2000 to explore the following questions: (1) To what extent did students appear to progress in their proficiency on the different standards over the course of the academic year?; (2) On which standards did students show the most growth? On which did they show the most difficulty?; (3) What were the benefits of using the standards to the learning and assessment processes?; and (4) What are the challenges in designing a reliable assessment system for teacher candidates' performance in their clinical practice? The authors focus on two aspects of professional learning for teacher candidates: (1) the consistent use of a clearly-articulated, well-understood, and developmentally-appropriate set of expectations for the knowledge and skills required by teacher candidates; and (2) the importance of a sound feedback and mentoring process to support the growth and development of candidates' teaching practice. (Contains 2 tables and 3 notes.)