ABSTRACT
This chapter discusses common mistakes in math instruction and explains the misunderstandings behind them. Jane used those base-10 blocks extensively while teaching addition and subtraction involving regrouping such as 35 − 18 and many other topics, and they worked very well. Now that it was time for her children to learn decimal numbers, she thought of those blocks again and wanted to take advantage of them in this new task. Changing the value scheme of base-10 blocks for the discussion of decimal numbers is not a good idea. In teaching her children about how to read a decimal, Jane tried to make a connection to their prior knowledge of fractions. In calculating decimal numbers, Jane's children often ended up with one or more trailing 0s after the decimal point such as 25.0. Jane's directions could be modified just a little to avoid misinterpretations on her children's part.
