A study by Clackmannanshire and Dundee University of pupils engaged in the philosophy for children (P4C) initiative claims IQ can rise by 6.5 points, putting children into a higher group at school.
When the average IQ is around 100, that is "pretty significant for the person concerned", according to Keith Topping of Dundee's education and social work faculty.
Steve Trickey, senior psychologist with the authority, said: "Schools are often judged on how pupils do in external examinations. The results we have should mean that the children will perform better in such examinations in five years' time. This is because the pupil's cognitive abilities test scores in primary school are strongly related to their subsequent examination attainments when they reach 16 years of age."
Clackmannanshire launched its programme two years ago prompted by Paul Cleghorn, headteacher at Sunnyside primary in Alloa. Mr Cleghorn went on to devise a Thinking through Philosophy programme which has been extended to 100 teachers and all primaries.
Pupils and teachers share a short story, picture or poem with the class acting as "a community of enquiry". Children generate their own questions which are discussed briefly by the whole group before they choose one for more intensive discussion.
The process involves critical questioning, linking questions, collaborative enquiry, building on others' ideas, reflecting, problem-solving, decision-making and summarising. Pupils are encouraged to show respect for other views and accept differences. Six and seven year-olds show they are as capable of critical and reflective thinking as older primary pupils.
Professor Topping said the study countered the arguments of some educators that improvement in thinking is impossible to measure. Outcomes were measured by norm-referenced tests of reading, reasoning and cognitive ability and by assessing self-esteem and child behaviour. Children and teachers filled in questionnaires.
Clackmannanshire says that improvements were found across children's verbal, non-verbal and quantitative reasoning abilities. "The possibility of such improvements occurring by chance was found to be less than one in a 1,000," it states.
The authority points out that children feel more confident and believe classroom behaviour has improved. "The fundamental aim of the programme is to promote more reasonable thinking and wiser decision-making in all children," Mr Trickey said.