This publication, comprising evaluative study results of the Northville, Michigan schools, illustrates the cost benefits of a 45-15 extended school year versus a traditional school year at the elementary level. Operational costs for elementary students are compared on a per pupil basis. Estimates from the Northville case study suggest that an operational cost saving as high as 5.1 percent can be realized using the extended school year. A worksheet is provided for readers to compute potential savings for their districts. Facilities and construction costs as well as start-up costs for implementing a 45-15 program are also discussed. (Author/DN)