Math Background

Modeling Subtraction: When Students Ask

  • Why should I learn subtraction?
    Lead children to see that knowing how to subtract saves time in calculating the change they should receive at a store; finding how many more miles, hours, or minutes are left in a trip; finding how many cookies will be left after they share some with a friend; or finding how many days, weeks, or months are left until their birthdays.

    Explain that knowing how to subtract will help them learn how to do more complex math later on.

  • Why do I need to learn the minus sign and the equals sign?
    Explain to children that math symbols are part of a language that everyone understands. Ask if anyone knows the names of these symbols in another language. Explain that even though different languages use different words for each symbol, the actual symbols and the numbers are the same worldwide so that people can communicate mathematically even though they speak different languages.
  • How do I know when to subtract?
    Review phrases and terms such as take away, how many are left, and difference. Remind children that whenever they are asked to take away from a group, they need to subtract. Make sure that children recognize the minus sign and know that it indicates subtraction.
  • Does the order of the numbers in a subtraction sentence matter?
    Hold up five connected cubes. Ask children how many cubes you are holding and whether or not you can subtract six cubes from this amount. If they say no, ask why not. If they say yes, remove the cubes one by one and then ask them what you should do when you run out of cubes. Explain that unlike the order of numbers in an addition sentence, the order of whole numbers in a subtraction sentence does matter! When your children study positive and negative integers, perhaps by using a thermometer, they will see that it is possible to do a subtraction like 5 − 6.
  • How will I know which number to write first in a subtraction sentence?
    Remind students that the number that is being subtracted from—that is, the number of items you began with—is written before the number that is being taken away.

Houghton Mifflin Math Grade 1