There are a number of issues involved in the validation of measures of teacher effectiveness, that is, a teacher's ability to promote student learning. Teachers' characeristics may be assessed at five different points: (1) pre-existing teacher characteristics--knowledge, skills, and attitudes which are necessary for success in the teacher education curriculum and as a teacher; (2) teacher competence; (3) teacher performance within a specific classroom setting; (4) student learning experiences; and (5) student learning outcomes. Further research is needed in classroom learning, classroom teaching, teacher competence, and the relationship between pre-existing teacher characteristics used for admission to teacher education schools and later competence. The validity of measures of teacher competence depends on the content validity of the measures of student learning outcomes used, and how well the outcomes attributable to the teacher are separated from the outcomes that are due to context factors. The expected gain score is useful in estimating the post-test score that a student with a specified pre-test score would achieve. A review of literature on teacher competencies led to the development and validation of a measure for Virginia's competency-based certification system. Seventy behavioral indicators of fourten teacher competencies resulted. (GDC)