The single-grade model of education, based on the division of labor in industry, has come to dominate the school, class, and curriculum organization used by central authorities. Although the multi-grade model is common in developing countries and in rural areas of industrialized countries, the knowledge required for effective multi-grade teaching is ignored and rendered illegitimate by those responsible for training and supporting teachers. This review presents five innovations in multi-grade teaching in developing countries. The Zambian experience is less than 10 years old and relatively small-scale. The Colombian experience with Escuela Nueva spans 3 decades and is large-scale. Both involve external agencies and support from the government mainstream. The Peruvian experience describes the multi-grade reality found among indigenous communities and the recent involvement of nongovernmental organizations in multi-grade teacher education programs. The fourth example, from Sri Lanka, illustrates how some problems faced by multi-grade teachers can be solved by recognizing that even mono-grade classes contain very wide differences in achievement and that a single grade may be conceived as a multi-grade context. The final experience describes Project Impact, which began as a radical reform of primary education in Indonesia and the Philippines and expanded to Liberia, Malaysia, Bangladesh, and Jamaica. Research on the outcomes and costs of multi-grade teaching is reviewed, and implications for the practice of multi-grade teaching are presented. (Contains 61 references and an annotated bibliography with 52 entries.) (TD)