Vocabulary extension immediately comes to mind when considering the development of thought, and so it should. With words being so central in the conduct and communication of thought, any increase in thought would normally lead to an increase in vocabulary. There is great scope for the practice of self-recording here, with the child taking responsibility for identifying a certain number of words each week that are new and specially interesting. If my concern is with concepts like contradiction, pressure or density, I must devise ways in which I can test their grasp of this new material. My preference is for a task which tests fresh application of the concept, and which tests whether the word is unselfconsciously part of the child’s active vocabulary.