Fantastic Online Manipulatives
I like the online manipulatives for students to see thier math in action. I especially enjoy the adding and subtracting link that allows students to see the "carry over" action of the manipulatives as they move from hundreds to tens to ones. This site improves my teaching as often I find we move away from using the manipulatives too soon and it can be cumbersome in grade four to have a bunch of hundred, ten, and one blocks for all students, this allows all students easy access!
How I Use It
I use it for those students who need to see in a visual way without the distraction of the blocks in front of them (falling off the table, etc.) students can see how the ones become tens and tens become hundreds. They can also see how the tens get 'broken' up as they go into the ones for subtraction. A really great way to show the "borrowing" and "carrying" of the traditional algorithum. The only drawback is that at times it can be difficult to get into the section you want to be in, you have to give very specific directions for students. I have used this site successfully with children in grades 1-6.