The Classroom Management Improvement Study (CMIS) tested the effectiveness of research-based classroom management principles and strategies in elementary school classrooms. Participating in the study were 41 teachers, divided into a treatment group that received a CMIS teacher's manual and participated in two workshops, and a control group. Half of the control group received the CMIS treatment in the middle of the school year to assess the effects of midyear intervention. Results indicated that teachers who received the CMIS treatment at the beginning of school implemented the recommended management strategies significantly more than did the control group teachers. Treatment in the middle of the school year had a limited impact on teachers' behavior. This report provides an overview of the CMIS: its background, treatment design, methodology and instrumentation, analyses of the major hypotheses and research questions, and discussion of the implications of the results for research on management and for teacher training. After the text, two-thirds of the document consists of 15 data tables and 14 appendices that include teacher workshop materials, a list of teacher manual contents, observer guidelines, all instruments, and teacher interview protocols. (MLF)