AimThis study evaluated a maths intervention programme, devised by the first author from psychological research into maths learning, difficulties, and intervention.MethodUsing a case series design, the first author collaborated with a Special Educational Needs and Disabilities Co-ordinator (SENDCo) and seven teaching assistants (TAs), who delivered the intervention to nine children (between four- and ten-years-old) of most concern to their teachers. Eight hours of training was provided for the adults, on the psychology of maths learning and use of a diagnostic assessment and intervention framework. Personalised intervention programmes were planned for the children. The adults worked one-to-one with the children, for 15–20 minutes a day, up to five times a week, over ten weeks. Researcher support and observational monitoring visits were provided each week. Pre- and poststandardised assessments were used to assess the intervention’s impact on the children’s maths achievement. Impact on the adults and children, and possible causal mechanisms, were explored through individual interviews.FindingsPre-/post-assessments, interview and observational data showed that children’s maths levels and attitudes had improved significantly. Thematic analysis evidenced that adults’ knowledge, skills, and confidence had increased.LimitationsLimitations include the small-scale nature of the study, coherence across structural elements (diagnostic assessment, framework, plans), lack of specific training on instructional methods, generalisability from out-of-class learning to classroom teaching, and problems associated with the operationalisation of mathematical constructs.ConclusionsThis study provides tentative evidence for the programme’s effectiveness, feasibility, and potential to address both moderate and severe maths needs, justifying larger-scale evaluation.