In 2003 Belfast Education and Library Board introduced an intervention programme COMET (Communication and Education Together) to tackle underdeveloped communication and language skills among primary school children from socially disadvantaged background. As children's language and communication skills can exert a significant influence on their learning as well as their social and emotional development, addressing this issue is of crucial importance. Applying a mixed-methods approach, this longitudinal study evaluates the effectiveness of the COMET intervention and examines its impact on the children's development of oral language skills as well as their reading performance. The quantitative data demonstrated the children involved in the programme had exhibited the higher levels of oral language skills as well as reading and reading-related abilities than the children who had not participated in the intervention. The children involved in the programme improved at a faster rate and had caught up with, or exceeded their peers who had not followed the COMET approach. The effectiveness of the COMET intervention was also confirmed by the qualitative data. The interviews with the principals, literacy coordinators, teachers and learning support assistants revealed that the intervention was an effective, valuable and very informative initiative that was manageable and functioned well in a highly complex and busy school environment. The findings of this study suggest that the COMET intervention is an effective and successful initiative, which not only assists the children in their development of oral language skills and reading abilities, but also positively contributes to reducing the gaps that exists between the children, providing them with a solid foundation and a greater chance for experiencing a school success.