TWO OF THE MOST IMPORTANT OPERATIVE DESIGN FACTORS GOVERNING SPEECH PERCEPTION IN CLASSROOMS HAVE BEEN EXAMINED AND GUIDELINES IN THE FORM OF GRAPHS, ETC. CONSTRUCTED THAT SHOULD BE UNDERSTANDABLE TO AND USABLE BY THOSE ASSOCIATED WITH SCHOOL PLANNING AND DESIGN. THE TWO FACTORS CONSIDERED ARE--(1) PROVISION FOR OPTIMUM REVERBERATION TIME, AND (2) PREDICTION OF SPEECH INTELLIGIBILITY (ARTICULATION) BY USE OF THE ARTICULATION INDEX. THE REQUIRED ADDITIONAL ACOUSTIC ABSORPTION TO PROVIDE OPTIMUM REVERBERATION TIMES IN A VARIETY OF CLASSROOM SIZES AND OCCUPANCIES IS SHOWN IN THE FORM OF GRAPHS. ARTICULATION INDEX IS A WEIGHTED FRACTION REPRESENTING, FOR GIVEN SPEECH AND NOISE CONDITIONS, THE EFFECTIVE PROPORTION OF THE NORMAL SPEECH SIGNAL AVAILABLE TO THE LISTENER FOR CONVEYING SPEECH INTELLIGIBILITY. CONSIDERED IN THE CALCULATIONS ARE THE NATURE OF THE SPEECH SPECTRUM, ATTENUATION OF THE SPEECH SIGNAL BEFORE REACHING THE EAR, AND THE EFFECTS OF NOISE IN MASKING THE SIGNAL. STARTING WITH KNOWN FACTS, AND ASSUMPTIONS, NOISE LEVEL LIMITS FOR EFFECTIVE SPEECH COMMUNICATION ARE DETERMINED FOR VARIOUS SPEAKER-LISTENER DISTANCES TYPICAL OF CLASSROOMS. USING THESE CALCULATED VALUES, GUIDELINES GRAPHS HAVE BEEN PREPARED WHICH SHOW WHAT SOUND TRANSMISSION LOSS PROPERTIES OF EXTERIOR AND INTERIOR WALLS ARE REQUIRED, FOR SEVERAL EXTERIOR NOISE CONDITIONS. CONSIDERATIONS ARE ALSO GIVEN FOR SOUND TRANSMISSION LOSS UNDER MAXIMUM NOISE LEVELS. (RK)