This study expands upon the extant prior meta-analytic literature by exploring previously theorised reasons for the failure of school-based, universal social and emotional learning (SEL) programmes to produce expected results. Eighty-nine studies reporting the effects of school-based, universal SEL programmes were examined for differential effects on the basis of: (1) stage of evaluation (efficacy or effectiveness); (2) involvement from the programme developer in the evaluation (led, involved, independent); and (3) whether the programme was implemented in its country of origin (home or away). A range of outcomes were assessed including: social-emotional competence, attitudes towards self, pro-social behaviour, conduct problems, emotional distress, academic achievement and emotional competence. Differential gains across all three factors were shown, although not always in the direction hypothesised. The findings from the current study demonstrate a revised and more complex relationship between identified factors and dictate major new directions for the field.