Systematic observation is a potent means of observing and recording classroom behaviours from which the appraisal of teacher vis-à-vis his efforts in the classroom could be done. Most instruments developed in the area of observation system are not based on science curriculum. Hence, this study employed critical construction and validation principles to obtain a Science Classroom Activity Schedule, SCAS, which is capable of recording verbal and nonverbal activities/behaviours typical of science lessons. These include: writing of the test items, determining the psychometric properties and ascertaining the applicability of the SCAS in the classroom. Tables, charts and graphs were used to illustrate the results of the analyses of the data obtained from the field’s trails. SCAS contains 28 items in categories. Norms and user’s manual were set to guide the use of this observation schedule. SCAS is useful for School Administrators and Inspectors of Education while performing their duties of monitoring and supervising the teaching and learning of science subjects in the schools. SCAS serves to meet various interests of classroom researchers and scholars.