What is the impact of garden-based learning on academic outcomes in schools? To address this question, findings across 152 articles (1990-2010) were analyzed resulting in 48 studies that met the inclusion criteria for this synthesis. A review template with operational coding framework was developed. The synthesis results showed a preponderance of positive impacts on direct academic outcomes with the highest positive impact for science followed by math and language arts. Indirect academic outcomes were also measured with social development surfacing most frequently and positively. These results were consistent across programs, student samples, and school types and within the disparate research methodologies used. However, a common issue was lack of research rigor as there were troubling issues with incomplete descriptions of methodological procedures in general and sampling techniques and validity in particular. Recommendations for more systematic and rigorous research are provided to parallel the growing garden-based education movement. (Contains 3 tables, 1 figure, and 1 note.)