A review of the critical literature provides a brief history of systematic observation of classroom behaviors, long valued as an important data collection method in educational research. Milestones in systematic observation of classrooms are traced back to 1914 and the development and use of the Special Strategies Observation System (SSOS) through a series of four phases is described. AEL revisions to SSOS Demographic Information, the SSOS Eight-Minute Observation Page, QAIT Assessment Instrument and the Classroom Environment and Resources Checklist are described. Extensive appendices document the revisions and include instruments, checklists, and forms.