The construct of student engagement is increasingly prevalent in the field of education, serving as the foundation of dropout prevention and high school reform initiatives. The purpose of this study was to further examine 1 measure of student engagement, the Student Engagement Instrument (SEI), designed to measure 2 subtypes of student engagement: cognitive and affective. This research extended the initial validation work on the SEI by examining score reliability and factorial invariance across grades and gender. Students (N = 2,416) were sampled from school districts in the rural Southeast and Upper Midwest of the United States. Results indicated similar factor structure, equal score reliability, and similar latent factor relationships across all grades. Evidence supported the contention that the SEI may be used at the middle and high school levels to measure cognitive and affective subtypes of student engagement. (Contains 5 tables and 2 footnotes.)