Academic affairs is the main mission that challenges the school administrators in ensuring that the learners have the required characteristics, especially when the academic affairs at the primary level in private schools cannot genuinely respond to the learners’ requirement, which reflects that the school administrators lack capability to drive the academic affairs to a higher level. The purposes of this research were to : 1) study level of academic administration competencies of private schools under Chonburi Primary Educational Service Area Office 1, 2) study the effectiveness level of private schools under Chonburi Primary Educational Service Area Office 1, 3) study the relationship between the academic administration competencies and the school effectiveness of private schools under Chonburi Primary Educational Service Area Office 1, and 4) create a predicative equation of the academic administration competencies affecting the school effectiveness of private schools under Chonburi Primary Educational Service Area Office 1. The sample used in this research was a group of 347 teachers in private schools under Chonburi Primary Educational Service Area Office 1 in the academic year 2018. The sample size was calculated using Krejcie and Morgan’s comparison table and proportionate stratified random sampling method. The research instrument was a five-level rating scale questionnaire with a reliability of 0.98. The statistics used for data analysis were : mean, standard deviation, Pearson product-moment correlation coefficient and simple regression analysis.