Student achievement test scores appear promising as indicators of teacher performance, but their use carries significant risks. Inappropriate tests improperly used may encourage undesirable shifts in curricular focus or poor teaching practices, and may unfairly favor teachers of more able classes. It is often said that standardized achievement test batteries are unsuitable for teacher evaluation, but few systematic alternatives have been suggested. The purposes of this paper are to analyze some problems in using student test scores to evaluate teachers and to propose an achievement-based model for teacher evaluation that is effective, affordable, fair, legally defensible, and politically acceptable. The system is designed only for detecting and documenting poor teacher performance; rewarding excellence in teaching is viewed as a separate problem, and is not addressed in this paper. In addition to pretesting and statistical adjustments for student aptitude differences, the proposed system relies upon attendance data and portfolios of student work to distinguish alternative explanations for poor test scores. While no single set of procedures can eliminate all errors, the proposed system, if carefully implemented, could expose teaching to constructive scrutiny, organize objective information about teaching adequacy, and help to guide its improvement.