Number Rack - Free on the Web and iPad
We think it's fantastic as a teaching tool for use on an Interactive Whiteboard as it facilitates the development of a child's number sense. Coloured beads are arranged in fives and tens. You can display up to ten rows of beads and there is a resizable shade which allows teachers to cover beads if necessary when modelling problems.
An additional feature with the iPad app is that it's possible to reverse the colours of rows 6 to 10.
There's also a free PDF document with teaching tips and suggested classroom activities. It's well worth downloading as it explores potential uses that you may not have thought of. We think Number Rack is great for demonstrating double digit subtraction, especially where decomposition is required, as it's so easy for children to see when you would need to exchange a ten for ones. That is just one of many potential uses so we recommend giving it a try.