Math Models and Tools
The Math Rack or Rekenrek
The rekenrek, or arithmetic rack, was designed by Adrian Treffers, a mathematics curriculum researcher at the Freudenthal Institute in Holland, to support the natural development of number sense in children.There are different versions of the math rack. Smaller versions, used in our primary grades consist of two rows of 10 beads. Larger versions with ten rows of ten beads are also available. Each row is made of five red beads and five white beads. This allows students to make mental images of numbers. Using 5 and 10 as anchors for counting, adding and subtracting is obviously more efficient than one-by-one counting. This tool provides learners with the visual models they need to discover number relationships and develop a variety of addition and subtraction strategies, including doubles plus or minus one, making tens, and compensation, thereby leading to automaticity of number sense.
Ten frames and dot cards can be used to develop students’ subitizing skills, the ability to “instantly see how many”. This skill plays a fundamental role in the development of students’ understanding of number. Two types of subitizing exist. Perceptual subitizing is closest to the original definition of subitizing: recognizing a number without using other mathematical processes. For example, a child as young as two might “see 3” without using any learned mathematical knowledge. Conceptual subitizing is being used when a person sees an eight dot domino and “just knows” the total number. The number pattern is recognized as a composite of parts and as a whole. The domino is seen as being composed of two groups of four and as “one eight”.
Open Number Line with Addition and Subtraction
The empty number line, or open number line as it is sometimes referred to, was originally proposed as a model for addition and subtraction by researchers from the Netherlands in the 1980s. A number line with no numbers or markers, essentially the empty number line is a visual representation for recording and sharing students’ thinking strategies during the process of mental computation. Before using an empty number line, students need to show a secure understanding of numbers to 100. Prior experiences counting on and back using number lines, recall of addition and subtraction facts for all numbers to ten and the ability to add/subtract a multiple of ten to or from any two-digit number are all important prerequisite skills.