The intent of this quantitative descriptive research was to determine if or to what extent a relationship existed between the leadership styles of principals of private primary schools in the Republic of Trinidad and Tobago and the achievement levels of their first, third, and fifth standard students who took national tests in language arts and mathematics. Six major questions and hypotheses guided this study. These were framed to determine if there were any statistically significant relationships between the leadership styles of the principals as measured by the Multifactor Leadership Questionnaire, Form 5X (MLQ-5X) and the achievement levels of students who took national academic assessments. Data were collected from 40 principals, 320 teachers, and the language arts and mathematics scores for approximately 2,600 students. These data were analyzed using linear regression analyses to determine whether relationships existed between the variables. Unlike previous research that resulted in definite positive or negative conclusions about all the relationships between leadership styles and student performance, the results from this study were mixed in terms of the statistical significance of the relationships between student achievement and principal leadership. No positive relationship was found between the leadership styles of principals and the achievement levels in language arts and mathematics for first standard students as well as for fifth standard students in the area of language arts. The null hypotheses were not rejected because no relationships were found between the MLQ-5X subscales, the leadership styles, and the scores obtained by the students. In addition, the null hypothesis, that MLQ-5X variables were not related to fifth standard math scores, was also not rejected primarily because only one of the multiple linear regressions showed some significance for mathematics. By contrast, in the case of the third standard students, the null hypothesis was rejected because, while the MLQ-5X subscales did not predict the percentile outcomes for that group, both transactional and transformational leadership styles were related to the language arts scores. Also, for mathematics, results of regression analysis revealed a significant relationship in terms of predicting the math percentile score for Standard 3 with the subscale, idealized influence behavior (11B), identified in this association. Transformational leadership significantly predicted performance in mathematics for this Standard 3 group. The outcomes of this study served to inform recommendations for school leaders, parents, and other stakeholders known to have some impact on education and schools in the Republic of Trinidad and Tobago. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]