Background. Evidence of maintained gains from thinking skills interventions are rare in the literature even within sectors of education, let alone across sectors.
Aims. This study investigated the cognitive effects of collaborative philosophical inquiry at long-term 2-year follow-up, after the participants had transferred to secondary (high) school without experiencing further philosophical inquiry in the interim.
Sample. Sample attrition was greater in the control than in the experimental group, but 96 experimental and 52 control subjects were available.
Method. Intervened children who engaged in collaborative inquiry for 1 hour per week over 16 months and whose pre-post cognitive gains were reported in Topping and Trickey (2007) were followed up 2 years later, some time after they had transferred from primary to secondary school, again using the Cognitive Abilities Test.
Results. The significant pre-post cognitive ability gains in the experimental group in primary school were maintained towards the end of their second year of secondary school. Higher achieving pupils were somewhat advantaged in sustaining these gains. The control group showed an insignificant but persistent deterioration in scores from pre- to post-test to follow-up.
Conclusions. Given the pattern of sample attrition, the group difference seems likely to be underestimated. The study provides evidence of maintained cognitive gains from collaborative philosophical inquiry, transferred across contexts. Implications for future research, policy and practice are discussed.