Evaluated is the validity of the behavioral categories held in common among three classroom observation systems. The validity model employed was that reported by Campbell and Fiske (1959) which requires that both convergent and discriminant validity be demonstrated. These procedures were applied to data obtained from the videotapes of 62 teacher trainees to ascertain their usefulness and applicability as a model for the validation of classroom observation systems. The validation procedures employed in this study were found to be an economical and useful method for examining the validity of all classroom observation systems. The advantages and limitations of the method employed are discussed. (Author)