The purposes of the study were 1) to validate the fitness of structural equation model of instructional leadership affecting school effectiveness with empirical data; 2) to study direct, indirect, and total effect of instructional leadership on school effectiveness; and 3) to test for measurement invariance in structural equation model across two sample groups. This research was quantitative. The sample included 270 schools under the Office of Roi Et Primary Educational Service Area 2. The research instruments included a five point scale rating questionnaire. Structural equation model was implemented. The results showed that: (1)The structural equation model of instructional leadership of school administrators affecting school effectiveness was fitted with empirical data. (2) Instructional leadership had direct, indirect, and total effects on school effectiveness. (3) Measurement of invariance between new administrators and highly experienced administrators showed a non-significant chi- square statistic and good practical values, indicating a one-factor model for both groups.