This study investigated possible sources of teacher change in the Stallings Effective Use of time (EUOT) staff development program administered to preservice teachers. These sources were: (1) the full EUOT program with feedback plus workshops; (2) feedback only; and (3) the trainer as post-treatment observer. Over a 15-month period, 20 student teachers participated in full treatment of feedback plus workshop, 7 participated in feedback-only treatment, and 23 served as control. Of the full-treatment group, 7 received one post-treatment observation by the trainer and another by an unknown observer, 6 received post-treatment observations by the trainer only, and 7 by an unknown observer only. The study measured change with 11 variables: 4 teacher-focused, 4 student-focused, and 3 class-focused. The paper concludes the EUOT program can have good application at the preservice level. Of the variables measured, student involvement in interactive teaching was the only one for which full treatment was significantly superior to feedback alone. Full treatment changed the ratio of interactive teaching by the teacher to interactive attending by the students, as opposed to rearranging time use. The findings discuss implications for teacher education and suggest areas of further research. (JD)