While some proponents of testing rest their hopes for stronger learning on the expectation that tests alone will motivate students to work harder, most posit that better learning will result primarily from better teaching--due to curriculum changes, greater attention to student needs, stronger teacher motivation, or focused investments in professional development, the hiring and retention of more expert teachers, and other school resources. This article examines the consequences of student accountability testing for: (1) the nature and quality of teaching, including the curriculum emphases and teaching strategies adopted in the classroom; and (2) the teaching workforce, including the quality of teachers who are recruited and retained in teaching in different schools and districts. The authors' review of the evidence on the consequences of various systems and approaches to accountability finds that the use of student assessment as a strategy for improving education has had positive influences on teaching and teacher quality; however, unintended negative consequences have also been found in systems that use limited measures and that emphasize sanctions without attention to improving school and teaching quality. The authors describe this evidence in relation to the characteristics of specific systems. They examine the various rationales for using students' tests to shape teaching and the teacher workforce, and they discuss recent research that has examined both the positive and negative consequences of using different approaches to using student testing. They evaluate these findings with attention to the nature of tests, the use of tests, and the stakes that are attached to test results. They conclude with a discussion of policy recommendations for the design and use of assessment systems that are likely to enhance rather than to undermine the quality of teaching.