A seventeen-month longitudinal study was made of adolescent pupils studying a modern world history syllabus. The pupils' ability to evaluate documentary evidence and to deduce concepts was measured and the change in their attitudes to aspects of the course was assessed. These cognitive and affective behaviours were related to the pupils' capacity to infer meaning from pictorial and documentary evidence and to draw the information so derived into a convincing synthesis. Significant gains were made on the skills, concepts and attitude tests. Oral testing showed that a substantial proportion of the pupils were able to draw meaning inferred from evidence into a convincing synthesis. A complex of cognitive and affective factors contributed to this mode of thinking. The investigation emphasises the importance of syllabus and teaching technique rather than maturation and intelligence and indicates the limitations of other researches into children's historical thinking based on a narrow view of Piaget's framework of cognition.