This study examined teachers' awareness of their classrooms' social networks, as reported by their students. Teachers and 549 students in 19 fourth- and 11 fifth-grade classes from 7 schools in 2 suburban/small urban school districts were asked twice during the school year to list the members of classroom social groups. In addition, we gave participants questionnaires to obtain teacher ratings of and peer nominations for student characteristics. Results indicated that teachers were most aware of classroom social groups that were also most salient to their students and overlooked fewer groups in spring than in fall. Comparisons of students in fully teacher-identified, partially identified, and completely overlooked groups revealed that they tended to differ in teacher- and student-perceived characteristics such as aggression and popularity. Knowledge of which students' social associations tend to be less easily detectable may be helpful to teachers as they endeavor to capitalize on and improve the social dynamics of their classrooms. (Contains 4 tables.)