Student engagement is an emergent research domain in educational psychology, as research increasingly supports the connection between academic achievement, school-related behaviours, and student engagement. In spite of the important role of student engagement in academic achievement across cultures, little is known about the cross-cultural validation of the factorial structure of students' school engagement instruments. This study explores the psychometric properties of The Student Engagement Instrument (Appleton & Christenson, 2004) in a population with a culture different from that in which the original version was developed and validated. The participants were 760 high school Portuguese students. Results confirm the factorial structure of the original version and reinforce the empirical support for a six-factor structure. However, some items loaded in different subscales, raising questions about the cultural specificities of the student engagement construct. (Contains 5 tables.)