116 ◆ Modeling Thinking
The Rekenrek
Figure 7.11 Rekenrek (Number rack)http://www.mathlearningcenter.org/web-apps/number-rack/Figure 7.12 Virtual Rekenrek (number rack)http://www.mathlearningcenter.org/web-apps/number-rack/The Rekenrek is a great tool for teaching a variety of strategies (see
Figures 7.11, 7.12, 7.13, 7.14 and 7.15). The Rekenrek (or counting rack) is
often neglected in the older grades, but it is a great tool to use for both
multiplication and division as well as multiplicative comparison problems.
When I am trying to introduce the three different types of multiplicative
comparison problems, I use the Rekenrek. It allows me to use small num-
bers so we can concentrate on the concept (later after the students under-
stand the problem, we can use larger numbers and we will have phased
out this scaffold).
Problem A: Sue has 2 marbles. Her sister has 2 times as many as she does.
How many does her sister have? How many do they have altogether?