The Classroom Sensory Environment Assessment (CSEA) is a tool that provides a means of understanding the impact of a classroom’s sensory environment on student behavior. The purpose of the CSEA is to promote collaboration between occupational therapists and elementary education teachers. In particular, students with autism spectrum disorder included in general education classrooms may benefit from a suitable match created through this collaborative process between the sensory environment and their unique sensory preferences. The development of the CSEA has occurred in multiple stages over 2 yr. This article reports on descriptive results for 152 classrooms and initial reliability results. Descriptive information suggests that classrooms are environments with an enormous variety of sensory experiences that can be quantified. Visual experiences are most frequent. The tool has adequate internal consistency but requires further investigation of interrater reliability and validity.