Objective: The School Site Needs Assessment instrument was designed to provide a multidimensional environmental scan of potential need for mental health services in classrooms and schools. Method: Items of the instrument covering various academic, social, and mental health domains were developed based on analysis of previous case management contact data and input from stakeholders. The teacher-response instrument was piloted with a convenience sample of 85 classrooms in seven schools. Results: 43% of students were observed by teachers to have at least one problem that could likely result in referral to a case manager. Frequently counted problems included “disruptive in class” (14% of students), “failing” risk (13% of students), and “hyperactive”-related behaviors (10% of students). Conclusions: The School Site Needs Assessment can assist school social workers in assessing the environmental mental health context of students and classrooms from the important perspective of teachers, leading to classroom and school site interventions.