It is a great mathematical software for children from third grade through college. Students get better understanding of some abstract things about math. There is a section you can try it free and get a feeling of it. Students can start making sense by making connection between numeric and graphic representations.
To get sketchpad non expiring license you need to pay$70 for 1-4 computers, but it gets cheaper as more computers are added. There are free webinars. There are also workshops and courses they offer.
The National Library of Virtual Manipulatives is a library of uniquely interactive, web-based virtual manipulatives or concept tutorials, mostly in the form of Java applets, for mathematics instruction (K-12 emphasis). The project includes dissemination and extensive internal and external evaluation.