This study evaluated the cost effectiveness of Instructional Support Teams (IST) in Pennsylvania, by comparing IST costs to those of traditional special education programs. An introduction notes pressures for change and the objectives of the prereferral intervention utilized in the IST approach. The study compared costs and program effectiveness of 1,074 schools in various phases of the IST process with those of a subset of the schools prior to IST implementation. Program effectiveness measures included the number of referrals to IST, the number of referrals for special education evaluation, number of special education placements, and number of same-year retentions. Cost measures included estimates of staff involvement, average salary and benefit costs, estimates of current and long-term costs, and extra costs of retentions. The study found that the IST had approximately equal costs to the traditional program. However, fewer students were placed in special education with the IST approach, and many more students with learning and behavioral problems were provided services than through the traditional program, indicating substantially higher effectiveness for the IST program than the traditional program. (Contains 15 references.) (DB)