Book excerpt: A short primer on each of the major math content areas that preservice and inservice elementary and middle school teachers are required to know. This book is an invaluable resource for the classroom teacher who needs both an overview for planning and help in answering student questions. Based broadly on the national standards, it gives the teacher general scientific information to cover most state's standards and to help prepare them for teacher certification exams. It also provides a strong overview of mathematical knowledge to allow the teacher to find information on important concepts, to see where significant moments in mathematical history fit chronologically, and to improve the teacher's understanding of mathematical ideas and concepts. Moreover, it saves professors from having to re-teach mathematics content so they can remain focused on the methods.