Throughout the years many studies (Blasé & Blasé, 1998, 2000; Elmore, 1995; Hallinger & Heck, 1996; Leithwood & Montgomery, 1982) have examined the concepts of instructional and collaborative leadership, as well as the relationship of the two leadership behaviors with school effectiveness. The researcher assumes that these two concepts are not mutually exclusive; they are highly interdependent and related with each other. The principals apply both in order to achieve school effectiveness and increase student achievement. Based on the above, the proposed study focuses on investigating the integration of the three concepts: instructional and collaborative leadership in relation to school effectiveness. It attempts to examine the validity of the assumption in schools that considered being successful/ effective; by investigating if these two leadership behaviors co-exist in reality and how principals put them into practice in order to achieve school effectiveness. Consequently, the main purpose of this research work is to develop a model through which the relationship between instructional, collaborative leadership and school effectiveness will be revealed. The major question under investigation is how school effectiveness can be achieved through the application of instructional and collaborative leadership. In order to address the above, a case study design will be applied. Data will be collected through semi-structured, open-ended interviews that will be conducted among principals in Cyprus secondary schools. Schools will be selected according to their effectiveness, which will be "measured" based on exams scores. The Ministry of Education organizes these exams for the high school graduates at the end of the academic year. Specifically, schools that experienced a significant exams scores increase the last three years during the leadership of the current principal will be the target population of this study. Twenty principals will be interviewed. The researcher assumes that the effectiveness of those schools is related to the principal leadership. The data collection will last for a month and is expected to take place during March 2005. Several important findings are anticipated to emerge from this research work. First, a new relationship and a model among the three concepts will be emerged. Secondly, since the assumption of the study reveals to be valid; the conceptual context and the conclusions of the study can be the base of other studies to further examine the previous in different educational contexts. If the results reject the assumption, reasons of this will be examined as well as how the integration can be achieved.To sum up, the study adds to the current body of literature providing a new concept that integrates two of the major leadership behaviors applied to achieve school effectiveness. Finally, it widens the opportunities for new educational practices and provides the foundation towards examining the possibility of moving towards an integrated approach in terms of school leadership behaviors.References Blasé, J., & Blasé, J. (1998). Handbook of instructional leadership: How really good principals promote teaching and learning. Thousand Oaks, CA: Corwin Press.Blasé, J., & Blasé, J. (2000). Effective instructional leadership: Teachers' perspectives on how principals promote teaching and learning in schools. Journal of Educational Administration, 38(2), 130-141.Elmore, F. R. (1995). Teaching, learning and school organization: principles of practice and regularities of schooling. Educational Administration Quarterly, 31(3), 355-374.Hallinger, P., & Heck, H. R. (1996). Researching the principal's role in school effectiveness: a review o empirical research, 1980- 1995. Educational Administration Quarterly, 32(1), 5- 44.Leithwood, K. A., & Montgomery D. J. (1982). The role of the elementary school principal in program improvement. Review of Educational Research, 52(3), 309-339.