Can Teach
Can Teach: Math Centers
This page offers a variety of math center ideas for general math and geometry. Instructions on setting up the center are not provided for most ideas, however, those lacking instructions are pretty self-evident.
Math Playground
Math Playground: Fraction Bars
Set the numerator and denominator and then see the fraction represented visually with a fraction bar.
Texas Instruments
Texas Instruments: Amazing Appetites
In this activity, students learn to count and solve original word problems. They learn to add by combining sets and subtract when removing the set. They use manipulatives to reflect the reasoning used in problem solving.