The purposes of this mixed method study were to (a) Examine the relationships among principal effectiveness, principal instructional leadership, and student achievement; (b) examine the differences among principal effectiveness, principal instructional leadership and student achievement; and (c) investigate what effective principals do to improve instruction and increase student achievement within their schools. All 585 pre-K through grade 5 elementary public schools in Indiana were included in the original sample. Phase 1 was quantitative using the Principal Instructional Management Rating Scale (PIMRS, Hallinger, 1983) to examine the perceptions of the principal's instructional leadership, the Principal Leadership Inventory (PLI; Downey, 1999) to measure principal effectiveness, and the Indiana standardized test (ISTEP) to look at student achievement. Statistical analysis of the data for the 232 schools that returned all of the instruments included descriptive statistics regarding the mean, standard deviation, frequency, and standard error. A Pearson product moment correlation, one-way independent measured ANOVA, one-way between subjects ANOVA, and standard multiple regression were used to test the study questions at a 0.05 level of significance. Findings indicated a teacher's perception of the principal's overall leadership ability makes no difference in student achievement data, but the teacher's perception of the principal's instructional leadership abilities does positively predict student achievement on standardized mathematics and English/language arts tests. Phase 2 was qualitative, identifying five more effective principals' schools whose standardized test scores were above predicted and above state average and three less effective principals' schools whose standardized test scores were below their predicted performance level as well as below the state average for site visits. The quantitative data in this study laid the foundation for the qualitative portion of this study informing the on-site, semi-structured principal interviews and separate teacher focus groups that explored what effective principals do to improve instruction and increase student achievement. Principals and teachers were asked the same open-ended, semi-structured interview questions. Keeping the focus group and interviewing questions in mind, themes for more and less effective principals could be grouped into four categories: (a) principal leadership characteristics, (b) instructional expectations, (c) procedures for change, and (d) measures of student achievement. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]