Background: There is now substantial evidence that language interventions delivered to small groups can be effective for improving language skills and hence strengthening the foundation for formal schooling. However, there are remaining challenges when delivering such interventions in naturalistic environments at scale. Method: We reflect on three randomised trials designed to evaluate the impact of an early years language programme, prior to the implementation of a large effectiveness trial, delivered in partnership with speech and language professionals. We consider findings within a framework from implementation science. Results: We found that, in contrast to policy-led interventions for reading and mathematics, language interventions are not prioritised in mainstream settings. Aside from this, other obstacles to delivery were the time taken to prepare and to timetable sessions, lack of communication about the requirements of delivery and the need for language screening. Crucial to success was the support from the class teacher of teaching assistants delivering the intervention. However, feedback was largely positive from most stakeholders, and the intervention was found to have a positive impact on children's language with preliminary evidence for effects on behaviour and on reading comprehension. Conclusions: While many educators recognise the importance of language for communication, the benefits of oral language interventions are only recently becoming prioritised by policy-makers. We propose that challenges to successful delivery and adoption of evidence-based language interventions in mainstream settings can be remedied through better communication with stakeholders and collaboration between researchers and professional colleagues including senior leaders, teachers, teaching assistants, speech and language therapists and psychologists. It is imperative to take account of issues of implementation when designing an intervention and to do this successfully is a multidisciplinary enterprise.