This study introduces the Schoolwork Engagement Inventory (EDA), which measures energy, dedication, and absorption with respect to schoolwork. Structural equation modeling was used to assess the validity and reliability of the inventory among students attending postcomprehensive schools. A total of 1,530 (769 girls, 761 boys) students from 13 institutions (six upper-secondary and seven vocational schools) completed the EDA 1 year apart. The results showed that a one-factor solution had the most reliability and fitted best among the younger students, whereas a three-factor solution was most reliable and fit best among the older students. In terms of concurrent validity, depressive symptoms and school burnout were inversely related, and self-esteem and academic achievement were positively associated with EDA. Boys and upper-secondary-school students experienced lower levels of schoolwork engagement than girls and vocational-school students.