The authors used a new multidimensional coding scheme to assess student learning engagement during 3 Grade 4 reading lessons. Students in 3 classes--2 in which students received integrated reading-science instruction and 1 in which they received traditional instruction--demonstrated moderate to high engagement in learning. However, students in the integrated instruction classes gained more in reading comprehension and reading strategy use during the 12 weeks of the study than did students in the traditional instruction class. Analyses of task complexity and practices that teachers used to scaffold students' cognitive processes and motivation suggested that measuring student engagement in conjunction with these variables may be critical for developing a deeper understanding of how academic gains are made. (Contains 6 tables and 5 figures.)