The Computerized Observation System (COS) is a software program which an observer can use with a portable microcomputer to document preservice and inservice teacher performance. Specific observable behavior such as appropriate questions and responses shown to increase student achievement are recorded as Low Inference Observation Measures. Time on task for student and teacher are also Low Inference Measures. The High Inference Rating Scale component of the COS measures a broad spectrum of teacher behavior currently used in teacher evaluation including enthusiasm, clarity, pacing, organization, oral communication, assessment, lesson objectives, behavior management, positive learning climate, and instructional methods. The Narrative Component is provided to record any pertinent information about the observation or setting that may be necessary for data collection, documentation, or recordkeeping purposes. The IBM convertible microcomputer was used for a field test of the program during the winter term of 1987, which was conducted with nine inservice teachers enrolled at Valdosta (Georgia) State College School of Education in a practicum on teaching students with behavior disorders. Discussions of the advantages and disadvantages of the IBM convertible and preliminary results of the field test conclude the report. Three references and lists of the goals of the school of education, the observer, and the teacher are included. (MES)