They learn what happens when you add or subtract multiples of 10 and 100. They develop good estimation strategies and are less likely to make the kinds of errors that result from the use of faulty algorithms. The Investigations curriculum provides many activities that develop knowledge about important landmarks in our system. The following are some specific examples that develop these ideas, throughout the grades. The focus in grades K and 1 is on counting, primarily by ones.
Teachers also see the beginnings of the use of landmarks as students play games and solve problems.
Whole investigations in grades 1 and 2 focus on counting by groups such as 2's, 5's, and 10's, as students figure out how many hands or fingers are in the room, count a set of squares, or play games involving money. Most of the addition and subtraction procedures students develop will be based on one of these two ideas. In grade 3 students also use cubes and 100 charts to skip count. They work with 100 and its factors, and solve problems about money, as they think about how to fairly share a dollar among several people. They explore multiples of 100 with money, the 300 chart, and the calculator, solve word problems, and make a 1000 chart and think about how to find numbers on it.