Abstract: Background: International debate around the best models of speech and language therapy provision for children with language disorders has highlighted the need for research into classroom-based approaches and intervention dosage. Working memory (WM) is a cognitive skill linked to attention and language. ‘Recall to Enhance Children’s Attention, Language and Learning’ (RECALL) is a novel, 6-week, classroom-based intervention delivered by health professionals (HPs) and teachers. It is designed to target WM and enhance attention and language skills in 4–5 year olds. Methods: A cluster randomised feasibility trial was conducted to investigate aspects of the feasibility of a definitive trial to evaluate RECALL: (i) recruitment and sampling procedures; (ii) compliance and fidelity; (iii) the acceptability of RECALL to HPs and teachers; (iv) the appropriateness of the outcome measures. Six classes of 4–5 year olds participated: two received RECALL, two received an existing intervention targeting attention skills (not underpinned by WM theory), and two received education as usual (no intervention). Ten children in each class (n = 60) were sampled to assess the appropriateness of the outcome measures. Classroom observations were conducted to measure fidelity and semi-structured interviews with HPs, and teachers explored the acceptability of RECALL. Results: The recruitment targets were met, and all six schools completed the trial, but the sampling procedures require modification. Compliance was good (95% of RECALL sessions were delivered), but fidelity to the intervention protocol varied between 76% and 45% across the two schools. This was influenced by large class sizes, child factors, and facilitator factors, e.g., their understanding of the theory underpinning the intervention. The lack of fidelity reduced the dose (number of practice items) accessed by individual children, particularly those most at risk. There were mixed findings regarding the acceptability of RECALL and the appropriateness of the outcome measures. Conclusions: The trial protocol could be easily scaled-up in a future definitive trial, with an amended sampling procedure. RECALL should be repackaged as a small group intervention to enhance the fidelity of its delivery and its acceptability to HPs and teachers. This study highlights the need for thorough training for professionals who deliver classroom-based interventions for children with language disorders. Trial registration: ISRCTN13633886. Registered on 7 September 2018