This research investigates the impact of collaborative work between an Educational Psychologist (EP) and teaching assistants (TAs) delivering a wave 3 National Numeracy Strategy (NNS) intervention. The aim was to decipher whether EPs can play a distinctive role in addressing the stubborn and significant tail of underachievement in numeracy and, indirectly, the associated risks to an individual's life opportunities, health, employability and social cohesion by providing consultative support for TAs. A multiple case study approach was adopted involving three case studies, each comprising one TA and three underachieving children, at different schools in the North of England. The EP modelled the use of the wave 3 NNS materials and supported/trained TAs in delivering this and other jointly agreed input over one academic term. Initial consultations were held with TAs to explore their experiences of mathematics and delivering numeracy interventions. Thereafter, joint planning and discussions took place on a fortnightly basis to identify what was working well and what input from an EP may be of use; EP input was provided as and when appropriate. Outcomes from the research were assessed using a standardized numeracy test, attitude questionnaires completed by TAs and children, interviews with TAs before and after the intervention and a research diary. The quantitative data gathered through the numeracy test and attitude questionnaires were compared pre and post intervention using descriptive statistics. The qualitative data from interviews and the research diary was analyzed using a thematic analysis approach.The results indicate that consultative support from EPs is welcome by TAs and schools and can be associated with positive outcomes for the children involved. TAs felt EP support was reassuring and acknowledged that it increased their knowledge and confidence and this directly affected the way they thought, felt and behaved in relation to the children's numeracy difficulties. TAs reported positive observable changes in the children's attitudes to numeracy lessons and there was a positive correlation between children's scores on the numeracy test and the final attitude scores allocated to them by TAs, indicating that the intervention had a substantial impact on children's attitudes and attainment in numeracy. TAs, parents and teachers attributed the positive changes seen in children to participation in the intervention and children's progress was clearly linked to the numeracy topics covered by the NNS materials. A model for EP-TA collaboration with NNS interventions is proposed and significant factors include: consultation; modelling resources; conducting diagnostic assessments; shaping TAs' pedagogical practice and providing training on instructional psychology methods.The research indicates that there is a potential distinctive role for EPs in raising the numeracy attainment and attitudes of children working with TAs on NNS interventions. The key element is successive EP consultations that target specific numeracy needs, effectively consider contextual factors and provide ongoing support for TAs. The proposed model could be applied to other numeracy interventions and provides an economical alternative to expensive SEN provision that EPs could usefully contribute to. Further research will be needed to ascertain more precisely the value added by the factors identified in this study to be associated with positive outcomes for children.