the students that they will find sums using the number line model. Then
display a large number line and a 5+4 domino, that is, a domino with 5
spots on the left side and 4 spots on the right. Then demonstrate with
a counter how a hop of 5 is taken on the number line. You may wish to
encourage students to count aloud as the hop is made. Then make a hop
of 4, starting at the place the counter landed. You might choose to
have them record what happened using the equation notation 5 + 4 = 9,
or to informally describe the moves this way: “If you take a hop of 5
spaces and then a hop of 4 spaces, you land on 9.” You may wish to
highlight the fact that in this model, spaces are counted, not points
on the number line.
After several trials, put the students in pairs and give each pair some dominoes, a counter, and individual number lines.
Ask the students to take turns moving the counter on the number
line to find the sum shown on the domino and recording the hops in
pictures and in equation form. Ask them to draw the first hop and write
the first numeral in green and the second hop and numeral in red.
Encourage the students to predict the sums and to verify their
predictions by moving a counter on the number line.
After allowing time for exploration, ask the students to
predict the answers to questions such as “If I take a hop of 3 and then
a hop of 5, where will I land?”  Now have students make up 2 similar
problems on a piece of paper and trade them with a friend. Students
should then solve their partners’ problems using the number line. When
the pairs have finished, call them together to discuss what they did.
Encourage them to use the number line in their explanation. Then ask
“If I take a hop of 5 and then a hop of 4, where will I land?"  "How
about if I take a hop of 4 and then a hop of 5?"  "Will this work
every time?" [Yes] Encourage them to explore the order property by
writing each first addend in green and each second one in red.
Be sure to lead a discussion about the order (commutative)
property. You may need to use other examples to illustrate this
important property of addition.
As a concluding activity, pose puzzles such as “I am the
number you land on when you take a hop of 5 and then a hop of 1. Who am
I?”  You may wish to encourage students to create and share similar
problems. One or more of these puzzles could be added to their unit