Chapter 3 introduces the concept of place value with finding groups of ten in a picture with more than ten similar objects. This leads to using ones blocks and tens sticks to represent numbers, to regroup more than 10 ones into a tens stick and the left over ones, and to modeling word problems with blocks and numbers. Chapters 10 and 11 cover two digit addition and chapters 12 and 13 cover two digit subtraction. This may be a bit late in the book, especially since, in the gap between chapter 13 and chapter 26, there is little opportunity to apply the arithmetical skills learned up through chapter 13, although there is some review and cumulative test problems. Because of the importance at this age of mastering addition and subtraction of multidigit numbers, a detailed description of the scope of adding such numbers follows.
Subtraction follows a parallel path, usually a chapter later.
As noted above, chapter 5 introduces the initial concepts of place value for ones and tens. 1 ten and 5 ones, which is represented both with blocks and tens sticks and with words as above. The next section builds on this by modeling 2 digit plus one digit addition, with extra ones blocks being grouped into a tens block, and numerical representations of the addition problems being given. This leads into a similar exercise on 2 digit plus 2 digit addition, and then to a lesson in which numbers are written in a vertical column, with special emphasis on alignment of similar places, although the actual addition is still done with blocks. Finally, in chapter 11, the formal carrying algorithm appears with the presence of a box above the tens place in which students write the carried digit.