Links Away
In this Unit Plan, students explore the
five models of subtraction (counting, sets, number line, balanced
equations, and inverse of addition) using links. They also learn that
the order property does not hold for subtraction and explore the
relation between addition and subtraction. Students also write story
problems in which subtraction is required and begin to memorize the
subtraction facts. A brief bibliography of related books for children is
provided.
The sequence of lessons in this Unit Plan builds an understanding
of the process and properties of subtraction.
Math Content
Students will:

Build
concrete, pictorial, symbolic, and verbal representations of
subtraction.
PreK2
This lesson, which focuses on the counting model for subtraction, begins with reading a counting book. The students model the numbers as the book is read. Then they make a chain of links and write in vertical and horizontal format the differences suggested by adding and subtracting one link at a time from their chains. Finally, they draw a chain showing one link being taken away and write in two formats the difference it represents.
PreK2
This lesson encourages students to explore another model for subtraction, the familiar set model. Reading one of the many books that feature subtraction set the stage for this lesson in which the students write story problems, find differences using sets, and present results in a table. In the discussion of the table, they focus on the effects of subtracting all and subtracting 0.
PreK2
In this lesson, students generate differences using a number line model. Because this model highlights the measurement aspect of subtraction, it is a distinctly different representation from the models presented in the previous lessons of this unit. The order property for subtraction is investigated. At the end of the lesson, children are encouraged to predict differences and solve puzzles involving subtraction.
PreK2, 68
This lesson encourages students to explore another model of subtraction, the balance. Students will use real and virtual balances. Students also explore recording the modeled subtraction facts in equation form.
PreK2
In this lesson, students explore the relation of addition to subtraction with books and links. Then the children search for related addition and subtraction facts for a given number. They also investigate fact families, including those where one addend is 0 and where the addends are alike.
PreK2
During this lesson, students use what they know about fact families to play a concentration game. They will also identify subtraction facts they need to learn.
PreK2
This final lesson reviews the work of the previous lessons and suggests a framework for summative assessment. Students will selfselect a solution strategy for subtraction from the models introduced in this unit. An extension activity is suggested in which students use the mathematical knowledge and skills developed in the previous lessons to demonstrate understanding and ability to apply that knowledge to playing a new game.