After the oft-repeated three Rs (reduce, reuse, recycle) comes the lesser-known but equally important fourth R: rot. In this case, rot means compost. Classrooms, schools, and school districts can use a number of methods to establish a compost program. The finished product is a valuable soil amendment that adds fertility to local farmland, school gardens, or classroom plantings. But what must be kept out of compost is as important as what should go in. Eco-Cycle, a nonprofit organization based in Boulder, Colorado, coordinates one of the oldest and most comprehensive school recycling and environmental education programs in the nation. In 2005, it created the Green Star Schools program, a national model for Zero Waste schools. Composting is integral to this project and to any Zero Waste effort in a school setting. This article outlines best practices that will help any school or school district launch a solid, effective composting program.