This study seeks to understand how numeracy and literacy learning occurs on a technology-supported personalised learning (TSPL) platform and the role of facilitation, design principles and social interactions in the learning process. The study evaluates an offline TSPL platform accessible on low-cost mobile phones in an afterschool setting in Kenya. The study design uses a design-based research methodology, and mixed methods approach to generate rigorous evidence on designing an effective TSPL intervention for maximising learning outcomes and feeds into the design of a large-scale, causal inference study planned for the future. This study also explores how learning on a TSPL platform can support the scale-up of the well-established Teaching at the Right Level (TaRL) methodology.