Ask students to think about the many strategies they have shared
and practiced in the lesson: counting on, counting back, counting
up, thinking addition, subtract zero, and making ten. Show
students the cards you prepared from the Subtraction Cards for Small Numbers
1–6 Masters and tell them that they are going to sort the cards by
their differences.
Tell students that a difference is the answer to a
subtraction problem. The activity is similar to the Sorting Sums
activity in Lesson 1, but take a few minutes to use the sorting
mat or chart paper to model sorting the subtraction cards as
shown in Figure 10. Encourage students to use connecting cubes,
ten frames, and number lines as tools as well as counting and
reasoning strategies.
Display the completed Sorting Mat chart from Lesson 1.
Challenge students to use the sums on the addition chart to help
them solve subtraction problems. Ask at least one pair of
students to complete the task using chart paper so that there
will be a record for class discussion.
Talk with student pairs as they work. Acknowledge the
effectiveness of their strategies and at the same time, encourage
them to try new strategies or tools to move them towards more
efficient strategies.
- How did you solve this problem?
- Which strategy do you like to use the most?
- I see you like to use [cubes to count up]. Have you tried using [name a tool or strategy student has not used]?
Give a smaller set to students who may be overwhelmed with the
task of sorting all 65 cards. The size of the numbers in the
problems on the six pages of the Subtraction Cards for Small Numbers
1–6 Masters increases from the first page to the last. So some
1–6 Masters increases from the first page to the last. Alternatively, you can choose to focus students'
thinking with particular sets of cards that will encourage
students to look for patterns or reinforce earlier learning. For
example, you can make a set that includes all the cards that
subtract one, two, or three, so students can practice counting
strategies. Using the set of cards that subtract zero can help
students see a pattern for these problems. To reinforce the work
on subtracting from 10, students can be given a set of cards
with these problems.
There are several ways to extend the lesson for students
who are already comfortable with these subtraction facts.
Challenge them to explain to other students good strategies for
solving the problems. Insist that their explanations be complete
and clear so that another student can use it to solve similar
problems. As you discuss students' strategies for placing cards
in particular groups, you can also challenge students to use the
same strategies with larger numbers. Finally, ask students to
look for patterns on the chart.
