The purpose of this study was to examine the validity and reliability of the Teacher School-Age Temperament Inventory (T-SATI) which is an adaptation of a parent version of the tool. A principal factor analysis using varimax rotation was performed on data provided by 143 teachers who reported on their 261 elementary school students. The results of the analysis supported the four hypothesized temperament dimensions: negative reactivity, task persistence, withdrawal, and motor activity. Cronbach's alphas of the dimensions ranged from 0.90 to 0.96. The T-SATI appears to have adequate validity and reliability. The T-SATI's research and practice applications are discussed. (Contains 4 tables and 1 figure.)