# Project: Nummer Kasten

I had introduced the nummer kasten in a previous post, which is used in Heguru class to teach the concept of addition and subtraction.

After a few classes, I had a better understanding of its usage, and decided to improve on my rather badly-made beta version.

Improved box
Here’s the new improved box, complete with different coloured sections (red and blue), with a slotted divider in the centre to allow balls to pass from one section to the next.

Opened nummerkasten

It comes with a sliding cover that allows me to reveal one portion at a time:

With sliding cover and balls

How to use
To give a clearer explanation of how the box is to be used to explain addition/subtraction, here’s an example using 3 balls.

I start by showing G that there are 3 balls, then place the balls one by one into the red section. I then close the box and shake it so that some of the balls fall into the other compartment.

Put 3 balls in the red side

Now, I slide the cover open again, revealing that there are 2 balls left on the red side. Usually at this point, G will open his eyes in wonder. 😉 I like that there is always the element of surprise, since we will not know how many balls to expect when the box is opened.

Only 2 balls left!

I will ask G to count the number of balls left in the red compartment, and where the remaining ball is. He has done this a few times to know that there is a separate compartment. I then ask how many balls there should be on the other side, then slide open to reveal the answer. 🙂

One on the blue side!

I find that the nummer kasten complements the dot bar, where the same concept is taught using blue and red dots on a 3×3 grid. The same equation is represented here:

Dot bar representation

This is one of the many interesting ways that the maths concept is presented in Heguru class, and I find that it brings the subject to life. I wish I had known of this method when I was teaching C, I wouldn’t have had such grief!

How do you teach maths?

## 15 thoughts on “Project: Nummer Kasten”

1. No Circ is Whole Son!

Thank you for another awesome idea! Love this! this will be in our school room very soon. Your blog is the first that I have visited repeatedly. Thank you for your help!

1. mummyshymz Post author

Hi, I simply used an empty cardboard box and stuck a piece of board in the centre, sized so that the ping pong balls can go through from one side to the other. For the cover, its another piece of board with flaps at the top and bottom (lengthwise). To enable the cover to be able to slide, I used strip magnets at the top and bottom of the box, and a few round magnets at the top and bottom of the cover. I covered the magnets so that the flaps would stick but not so strongly that the cover would not be able to slide easily. The back is just construction paper. Do select a sturdy box so that the box will not go out of shape 🙂

2. Shahida

I’ve tried this out and it doesnt turn out as great as yours but still i love it! Thanks for sharing! 🙂