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### Using the Number Line to Compare

Pre-K-2

In this lesson, students determine differences using the number line to compare lengths. Because this model is based on linear measurement, it is a distinctly different representation from the models presented in the previous two lessons. At the end of this lesson, children are encouraged to predict differences and answer puzzles involving subtraction. ### Balancing

Pre-K-2

This lesson encourages students to explore another model of
subtraction, the balance. This model leads naturally to recording with
equations. Students use actual and virtual pan balances in their
explorations and record the modeled subtraction facts and the related
addition facts in equation form.### Fact Families

Pre-K-2

In this lesson, the relationship of addition to subtraction is explored with books and with connecting cubes. Students search for related addition and subtraction facts for a given number using a virtual or actual calculator to find differences. They also investigate fact families when one addend is 0 as well as when the addends are the same.### Comparing Columns on a Bar Graph

Pre-K-2

During this lesson, students apply what they know about comparison subtraction by constructing bar graphs and using the graphs to answer questions.### Looking Back and Moving Forward

Pre-K-2

This final lesson of the unit reviews the work of the previous lessons and suggests a framework for summative assessment. During this lesson, students use the mathematical knowledge and skills developed in the previous lessons to demonstrate understanding and the ability to apply that knowledge to playing subtraction games.### Counting to Find Sums

Pre-K-2

This lesson focuses on the counting model for addition and begins with
reading a counting book. Students model the numbers with counters as
the book is read. Then they count the spots on each side of a domino
and write, in vertical and horizontal format, the sums suggested by
dominoes. Finally, the students illustrate a domino and record a sum it
represents.### Hopping on the Number Line

Pre-K-2, 3-5

In this lesson, students generate sums using the number line model.
This model highlights the measurement aspect of addition and is a
distinctly different representation of the operation from the model
presented in the previous lesson. The order (commutative) property is
also introduced. At the end of the lesson, students are encouraged to
predict sums and to answer puzzles involving addition.### Exploring Adding with Sets

Pre-K-2

This lesson builds on the previous two lessons and encourages students
to explore another model for addition, the set model. This model is
similar to the counting model in the first lesson, because it is based
on counting. Reading a related counting and addition book sets the
stage for this lesson in which students write story problems, find sums
using sets, and present results in the form of a table. In the
discussion of the table, the students focus on the order property and
the effects of adding 0.### Balancing Discoveries

Pre-K-2

This lesson encourages students to explore another model of addition,
the balance model. The exploration also involves recording the modeled
addition facts in equation form. Students begin to memorize the
addition facts by playing the “seven-up game.”### Seeing Doubles

Pre-K-2

In this lesson, the students focus on dominoes with the same number of spots
on each side and on the related addition facts. They make triangle-shaped flash
cards for the doubles facts.