The Practical Mechanics in Primary Mathematics Project is an Australian research Council large grant funded project investigating the teaching and learning of force and motion concepts in the upper primary school. While the project is primarily focussed on practical activities and the mathematics necessary to model them, other aspects of learning are also being critically examined. One of these aspects is the extent to which children can explain and defend their understandings of the physics involved in the understandings. As part of the data collection the children are required to complete a reflective statement " What I learned in this lesson ....". In this paper we look at the reflective statements that the children have written, and analyse these with respect to what the children say that they have learned. These reflective statements are then compared to an objective assessment of what they have learned, the "Tapping Students' Science Beliefs" assessment instrument. The results of this study provide some answers to the question "Do children know what they know?", answers that have implications for both teaching and assessment.