We examined the effects of a professional development intervention that included data-based performance feedback delivered via electronic mail (e-mail) on preschool teachers' use of descriptive praise and whether increased use of descriptive praise was associated with changes in classroom-wide measures of child engagement and challenging behavior. A multiple probe single-subject experimental design across four preschool teachers was used. Following a brief training session on the use of descriptive praise, coaches observed each teacher conduct a large-group activity and sent them e-mail messages containing performance feedback with a hyperlink to a descriptive praise video exemplar. Training plus e-mail feedback was associated with increases in teachers' use of descriptive praise for each of the four teachers. Challenging behavior decreased somewhat as teachers' use of descriptive praise increased. Class-wide measures of children's engagement remained relatively stable across baseline and intervention phases. Implications for future research and practice are discussed. (Contains 4 tables and 2 figures.)