Providing substitute teachers in large school districts usually requires both an extensive organizational structure to coordinate substitute teacher demands with available supply and a large operating budget. In addition, the temporary nature of the substitute teacher position tends to preclude their effective integrating into regular school district inservice programs. The replacement of present substitute teacher procurement practices by a permanent pool of substitute teachers has been suggested as one possible method for improving substitute teacher quality and morale as well as reducing school district cost. This study demonstrates how Monte Carlo techniques might be utilized to determine the optimal size for a substitute teacher pool in a given district where optimal size is defined as (1) the size required to minimize cost to the district, (2) the size required to maintain present substitute teacher service levels in the district, and (3) the size needed to financially break even with the current substitute teacher program. Both uniform and non-uniform by day in the school week substitute teacher pool sizes were calculated for a school district using this technique. The results of the study strongly suggest that not only might permanent substitute teacher pools result in their better integration into regular school district programs, but substantial cost savings might also result.