This study compared self-contained and regular classrooms for the quantity and quality of instruction provided to students classified as emotionally disturbed, learning disabled, and educable mentally retarded. The study compared 22 effectiveness indicators within 6 modifiable dimensions of instructional variables: (1) questioning style, (2) classroom climate, (3) academic learning style, (4) individualization, (5) teaching style, and (6) classroom management. Observations in 45 special classes were compared with a sample from a database of 1500 observed regular classes using the Classroom Observation Keyed for Effectiveness Research observation system. No differences between regular and special education teachers were found in three indicators: teachers' ability to work with varied groups, to give clear directions, or to use positive reinforcement. Significant differences were found on 19 other effectiveness indicators. Differences favored regular class teachers in three dimensions: questioning style, classroom climate, and academic learning style. Differences favored special education teachers in two measures of individualization. Most teaching style differences favored regular class teachers. For the dimension of classroom management, regular classes showed more evidence of effective management, but special educators assisted students with error correction more. Tables present details of the study's findings. (Contains 41 references.) (Author/DB)