Nigeria is home to more out-of-school (OOS) children than any other country on Earth. More than 10.2 million children match that description throughout Nigeria, a conflict-affected country that grapples with long-standing challenges of entrenched poverty and weak governance. We used a randomized control trial (RCT) with 1,723 out of school children, ages 9-14 (850 treatment and 873 control), to determine the impact of an accelerated learning program (ALP) on the literacy, numeracy and social-emotional learning (SEL) outcomes of OOS children in Northeast Nigeria and gathered qualitative and costing data to determine stakeholder's experiences with the program and the cost of implementation. Results show that at an average cost of 66 pound (2018 GBP) per child for 7 months of service, the program had positive, small to medium, and statistically significant effects on children's literacy and numeracy skills, but no effects on SEL outcomes. We include subgroup analysis to identify baseline equity gaps and the differential impact of the intervention by gender, displacement status and mother tongue language. We discuss limitations and policy and practices implications of these findings.