Math Background

Lesson: Modeling Subtraction
Introducing the Concept

Children first learn the concept of subtraction as “taking away” by subtracting from numbers to 6.

Materials: overhead projector, 6 counters, number cards for the numbers 0 to 6 and the minus sign and equals sign

Preparation: Prepare number cards for 0 to 6 and the minus sign and equals sign.

Prerequisite Skills and Concepts: Children should be proficient in counting and recognizing numbers to ten. They should also have experience finding sums to eight.

  • Say: I would like volunteers to help me act out a story.
    Have five girls come up to the front of the classroom.
  • Ask: How many girls are at the front of the room?
    Children should say “five.” Have 1 boy come up to the front of the room.
  • Ask: How many boys are at the front of the room?
    Children should say “one.”
  • Say: Let's add 5 + 1 to see how many children in all are at the front of the room.
    Elicit that there are 6 children at the front of the room.
  • Ask: What did we do when we asked one boy to join the group?
    Children should say that one was added or the group was made one larger. Ask the boy to sit down.
  • Ask: How many children sat down?
    Children should say “one.”
  • Say: Six children were at the front of the room and one child sat down. Let's count how many children are left at the front of the room.
    Have the children count aloud to 5.
  • Ask: What did we do when we asked one child to sit down?
    Children should say they took away 1 child or made the group smaller by one. Continue bringing boys and girls up to a total of 6 to the front of the room and then asking one of the children to sit down. Have the class count to find the difference.
  • Ask: What did we do each time?
    Children should say that they took away from the group.
  • Say: When you take away from a group, you are subtracting. Now let's do this with counters.
    Direct the children to look at the overhead. Put 5 counters on the overhead projector.
  • Ask: How many counters are there?
    Children should say “five.”
    Take away 2 counters.
  • Ask: If I take away 2 counters, how many counters are left? (3)
    Continue placing up to 6 counters on the overhead, removing some and having the children count to find how many are left.
  • Say: Now let's learn how to write subtraction sentences.
    Put four counters on the overhead.
  • Ask: How many counters are there?
    Children should say “four.” Write 4 on the overhead.
  • Say: Now let's subtract or take away one counter.
    Remove one counter and write 1 on the overhead.
  • Ask: How many counters are left?
    Children should say “three.” Write 3 on the overhead.
  • Say: We can show that we subtracted by using math symbols.
    Write a minus sign between the 4 and the 1.
  • Say: This is a minus sign. It tells us that we are subtracting. Can you make a minus sign with your fingers?
    Model making a minus sign with your fingers. Point to the area on the overhead where the equals sign belongs.
  • Ask: What sign can we write here to show that 4 − 1 (point to 4 − 1) and 3 (point to 3) are the same?
    Children should say that an equals sign should be written.
  • Say: That's right. We use the equals sign in both addition and subtraction to show that numbers on either side are the same amount.
    Continue as above, modeling different subtraction sentences with counters and recording them. You may wish to have students volunteer to hold the number cards and the symbol cards that represent the subtraction sentences that you are modeling.

Houghton Mifflin Math Grade 1