Research studies have found a number of teacher-related variables that are associated with student achievement. Professional development activities designed to improve the knowledge and skill of teachers can help students improve academically. In investigating the motivation for professional development, the findings of several researchers support the conclusion that teachers are motivated to participate in continuing professional development activities primarily by intrinsic factors. Evaluation results of an Australian inservice program for educational administrators indicate that well-designed continuing professional development programs can change the behavior of participants. In addition, research on effective schools has shown the important role of the school principal in encouraging and supporting the continuing professional development of teachers. Several elements essential for or conducive to effective professional development programs are identified and discussed briefly. A 17-item bibliography is appended. (MLF)