Background: Development of socio-emotional competencies is key to children's successful social interaction at home and at school. Aims: This study examines the efficacy of a UK primary school-based intervention, the Pyramid project, in strengthening children's socio-emotional competencies. Sample: Participants were 385 children from seven schools in two UK cities. All children were aged 7-8 years and in school Year 3. Children were screened for socio-emotional difficulties through the Strengths and Difficulties Questionnaire (SDQ; Goodman, 1997) and a multi-agency meeting of relevant professionals before being allocated to attend a Pyramid Club intervention ("n" = 103) or a comparison group ("n" = 282). Method: A 2 x 2 mixed-model design was used: group (intervention group vs. comparison group) x 2 time points (pre- vs. 12 weeks post-intervention) with repeated measures on the time factor to investigate the impact of the Pyramid Year 3 intervention. Teachers completed the SDQ-T4-16 for all children pre- and post-intervention to measure participants' socio-emotional health status. Results: As measured by the two SDQ difficulty sub-scales of Emotional and Peer problems and the SDQ strength sub-scale of Prosocial behaviour, post-intervention improvements in the Pyramid attendee group were of greater magnitude than those of the comparison group. Conclusions: The Pyramid project intervention improves the socio-emotional health of vulnerable children through promoting positive outcomes as well as reducing socio-emotional deficits. These findings further support the inclusion of a salutogenic approach in promoting children's socio-emotional well-being. (Contains 3 tables and 2 figures.)