The influence of change in teachers' instructional effectiveness upon the relationship between their expectations for students' performance and student achievement outcomes is investigated. Data were gathered from 44 intermediate and high school level teachers who particpated in an inservice training workshop on mastery learning strategies. Correlations between teachers' initial expectations for students' achievement and students' final examination scores, final grades, and teachers' follow-up expectations for students, were all significantly lower in mastery classes of those teachers who experienced some positive change in their instructional effectiveness. The degree of change in instructional effectiveness was determined by comparing each teacher's mastery and control classes in terms of the following two outcome measures: (1) percent of students in each class receiving an A or B as course grade; and (2) average percent correct on a common course examination. Implications regarding related teacher perceptions and classroom behaviors are discussed. (Author/RL)