Subtraction Strip Board

Subtraction reverses the journey. A gray strip covers the minuend's excess, and the subtrahend strip retreats from the total. The child sees what remains.

• Framework: Montessori
• Unit: Mathematics
• Learning area: Subtraction
• Level: Ages 5-6

Objectives

• Perform subtraction within 18 using colored strips
• Memorize subtraction facts through sensorial practice
• Understand subtraction as 'taking away' along a number line
• Bridge to abstract subtraction

Materials

• Wooden board numbered 1-18 along the top
• Gray strip to cover unneeded numbers
• Blue strips 1-9
• Red strips 1-9
• Recording paper

Instructions

1. Choose a minuend, say 9. 2. Cover numbers 10-18 with the gray strip. 3. Choose the red subtrahend strip, say 4. 4. Place it at the right edge, ending at 9. 5. Read the remainder: the first uncovered number is 5. 6. Record '9 - 4 = 5.' 7. Systematically work through combinations. 8. Notice that subtraction is not commutative. 9. Discover the connection to addition: 9 - 4 = 5 because 4 + 5 = 9.

Educator tip

Always introduce subtraction after addition is secure. Let children discover the addition-subtraction connection rather than announce it.

Assessment

Note systematic coverage, accurate recording, and growing awareness of the addition-subtraction relationship.

More from Mathematics

• Multiplication Bead Bars
• Division with Bowls and Beads
• Introduction to Fractions — The Fraction Circles
• Addition and Subtraction of Fractions
• Multiplication Short and Long Chains (Squaring and Cubing)
• Small Bead Frame
• Binomial Square — Algebraic Pattern
• Geometry — Study of Lines