Teamwork is very important for successful and efficient operations. Accomplished administrators need to develop their team to be in unity and work voluntarily and willingly. The proposes of this research were to study and compare the role of teamwork of school administrations under Prachinburi Primary Educational Service Area Office classified by educational service area and school size. The sample was a group of 335 school administrators and teachers in Prachinburi province determined by Krejcie and Morgan’s table and proportionate stratified random sampling. The research instrument was a five-level rating scale questionnaire with a discrimination of between 0.20-0.74 and a reliability of 0.87. The statistics used for data analysis were: percentage, mean, standard deviation, T-test, One-way ANOVA and Scheffe’s paired difference test.