Survival rates for paediatric brain tumours have risen, but radiation treatment can leave many children suffering from long term cognitive impairment impacting learning and behaviour. This 16 week study investigates the drug Metformin, already widely used for diabetes, to see if it can promote cognitive recovery and brain growth in children treated for medulloblastoma. By testing if this safe medicine can “repair” the brain after radiation, researchers hope to improve the quality of life and long term thinking skills for survivors of aggressive brain tumours.