Results of a questionnaire on instructional leadership administered to elementary school principals and teachers in California confirmed literature findings that instructional leadership behavior significantly influences student achievement. The study sought to determine (1) the 29 most important instructional leadership behaviors through literature review and expert opinion, (2) the degree to which principals implement these behaviors in high- and low-achieving schools, and (3) the behaviors' effect on reading and math achievement. The questionnaire was sent to respondents from schools with differing achievement scores on the California Assessment Program. The 510 returned questionnaires represent a response rate of 60 percent. Ten tables present data findings. The 29 "most important" of 44 commonly identified instructional leadership behaviors were compared in frequency between high-achieving schools (HAS) and low-achieving schools (LAS). Discoveries include the following observations: (1) HAS teachers rated their principals as demonstrating 10 instructional leadership behaviors more often than did LAS teachers, including goal communication and frequent classroom visits; (2) HAS teachers perceived that their principals performed six functions associated with the principal role more often than did LAS teachers; and (3) HAS principals' 10 behaviors should be studied for validation among "effective" schools. Instructional leadership models, experts' ratings, and a six-page bibliography are appended. (CJH)