One of the most impressive language developments in the early school years is the astonishing growth of vocabulary. Children enter school with the ability to understand and produce hundreds or even a few thousand words, and thousands more will be learned at school. In both the spoken and written language at school, words such as ‘homework’ or ‘ruler’ appear frequently in situations where their meaning is either immediately or gradually revealed. Words like ‘population’ or ‘latitude’ occur less frequently, but they are made important by their significance in academic subject matter.