Based on the theory of change, we gather, organize, and synthesize the evidence on the impact of three language of instruction (LOI) choices (teaching in mother tongue [MT] with later transition, teaching in a non-MT language, or teaching in two or more languages at one time) on literacy and biliteracy outcomes. We focus on quantitative and qualitative studies of LOI interventions in low- and middle-income countries (LMICs) and consider languages that are commonly spoken in the developing world. As such, we include studies that examine transfers from local languages to English, but not those evaluating transfers from local languages to languages that are less spoken in LMICs (e.g., Swedish).