Using a 100-bead abacus in elementary math
One of the best manipulatives for first and second graders is a simple "school" abacus (or 100-bead abacus) that has 10 wires and 10 beads on each wire.
This doesn't mean a Chinese or Japanese abacus with a special counting system. I am talking about using a simple 100-bead abacus for counting, and treating each bead as 1. You don't have to learn any of these sophisticated systems that have been in use with various abacuses. Just consider each bead being 1, period.
You have 10 tens, or a hundred, in your abacus, and that goes a long way in explaining tens and ones or 2-digit place value to children in kindergarten and first grade.
It is best if the abacus has five beads in alternating colors, like on the abacus in the right. Then the child will easily recognize 6, 7, and 8 beads without counting.
Ideas on how to use the abacus
- Learning numbers. Play a simple game with the abacus. When it's your turn, you say a number, such as 42, and the child "makes" it or shows it on the abacus. Then the child says a number for you and you show it on the abacus. Continue taking turns like this.
- Going over 10 in addition. Choose for example 6 beads on one wire and 8 on the next one. You can show how the five and five on those two wires makes ten, and some are left over.
- Patterns in subtraction (and addition). Show the student how to do each of the subtractions
10 − 5
20 − 5
60 − 5
The student will notice they are very similar — there is a pattern!
- Adding 2-digit numbers without regrouping (carrying). To add 23 + 45, a child can move 2 tens and 4 tens, then 3 and 5 individual pieces. You can show the child how to add the tens and ones separately.
- The idea of regrouping. Let the child explore what happens with 28 + 9 and other sums that require regrouping.
- Model multiplication. For example, move 4 beads on each of the 5 neighboring wires, and there you have 5 times 4!
- Model division. Please see the post Abacus and basic division for more details.
So this is not rocket science; it is very easy! You can browse Amazon's abacus selection here.