Children are very curious about the world around them. You may find them peering at tadpoles in a pond, counting ants on a log, or wondering about the stars, the sun, and the moon. I have been asked many times: Is the moon really made of cheese? Do astronauts live on the moon? Why does the moon look different every time I look up? Introducing…

Recent educational research has turned increasing attention to the structural development of young students' mathematical thinking. Early algebra, multiplicative reasoning, and spatial structuring are three areas central to this research. There is increasing evidence that an awareness of mathematical structure is crucial to mathematical competence…