Currently, most of the administrators are facing problems of applying suitable leadership style in their administration, reported by the Educational Work Unit. Therefore, applying suitable leadership may assist administrators to solve the confusion due to the overlapping of work occurred in work practice, administration, and ordering or commanding among the top level of management team work unit. The Path-Goal Theory was used as the main theory to support this study. The objectives of this study were to investigate the leadership styles of school administrators that affecting teacher effectiveness. This study employed quantitative method survey design using questionnaire as an instrument. Simple random sampling technique was utilized in this study. A total of 254 administrators and teachers from schools under the Office of Kalasin Primary Educational Service Area 1 were involved as respondents. Data was analyzed using frequency, percentage, mean value, standard deviation, correlation Pearson product moment, and multiple regression Stepwise method. Findings showed that there are two types of leadership styles of school administrators, namely supportive leadership and participative leadership styles which have significantly affecting teacher effectiveness. In addition, both leadership styles have been jointly predicted teacher effectiveness at 56.80 percent at the significance level as 0.01. In conclusion, in order to increase teachers’ working effectiveness, administrators should promote, practice, and improve these two leadership styles, namely supportive leadership and participative leadership styles regularly.