This project examined the extent to which varying instructional grouping arrangements are used for different categories of mildly handicapped students in various instructional settings and the extent to which any differences translated to differences in student responses. Observational data were recorded all day in 10-second intervals for 122 elementary students categorized as learning-disabled, emotionally/behaviorally disturbed, educable mentally retarded, and nonhandicapped, in mainstreamed, resource room, and self-contained programs. While handicapped students, in general, received more instruction in individual arrangements, usually in the special education setting, the only category effect that emerged was that mentally retarded students in self-contained placements spent a greater proportion of special education time in entire group instruction. Differences in instructional grouping arrangements translated to differences in student responding, with active responding and academic engaged times significantly higher during individual instruction, compared to entire group and small group instruction, in both mainstream and special education settings. (Author/JDD)