A cost-benefit analysis based on existing green schoolyards in California compared a green schoolyard prototype with a gray schoolyard prototype. Over a 20-year period, the green schoolyard's cumulative net cost was 381% less than the gray schoolyard. The prototypical green schoolyard would yield at least $600,000 in net benefits related to increased student attendance, improved academic performance, increased staff retention, and savings in building heating and cooling costs (breaking even at 9 years), while the gray schoolyard would yield no benefits over time.