Background: Building 'key skills' may help prevent the development of challenging behaviour in children with an intellectual disability. The aim of this paper was to extend the current limited evidence in this area. Method: We undertook two studies with children with an intellectual disability in school settings: (1) a cross-sectional replication study exploring the relationship between 'key skills' and challenging behaviour. (2) a longitudinal study follow-up exploring change in 'key skill' levels and challenging behaviour. Results: The replication study recruited 74 participants, those scoring lowest in 'key skill' had a 94% chance of having challenging behaviour; those with the highest scores had a 6% chance. The follow-up study recruited 39 participants, we found a significant increase in children's 'key skill' level (p < 0.001) and a decrease in their challenging behaviour (p = 0.046). Conclusion: Building 'key skills' in children with an intellectual disability may help reduce or prevent challenging behaviour.