This intervention study was conducted to document conditions under which a computer based literacy game (GraphoGame™) could enhance literacy skills of first grade students in an African city. The participants were first grade students from Government schools (N = 573). These students were randomly sampled into control (N = 314) and various intervention groups (N = 259). GraphoGame™ was administered on cellphones to students at their schools under supervision. Each student in the study was assessed using a battery of locally developed cognitive tests that measured emergent literacy skills (Orthography test), decoding competence (Spelling test), vocabulary (Picture Vocabulary Test—PVT) and arithmetic (Zambia Achievement Test—ZAT). There was a positive effect of the game for the Spelling test—which closely targeted the skill GraphoGame™ is designed to promote. The most effective intervention combined exposure of both the teachers and the students to the game. Initial letter knowledge was a good predictor of final letter knowledge on GraphoGame™.