Khan Academy
Khan Academy: Cross Sections of 3 D Objects
Practice your knowledge of all possible cross-sections of common 3D objects. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
Better Lesson
Better Lesson: Tree Mapping in 2 D
Identifying 2D shapes in common objects and sorting according to shapes connects the real world to learning shape names and attributes.
PBS
Pbs: Mathline: Let's Face It [Pdf]
Check out this math project about polyhedra! Learners will enjoy the hands-on activity while they learn about tetrahedrons, hexahedrons, octahedrons, dodecahedrons, and icosahedrons. [Requires Adobe Reader.]
National Council of Teachers of Mathematics
The Math Forum: The Cylinder Problem: Middle School Lesson
This lesson offers an interesting, hands-on experience for middle school students studying cylinders. Students will create cylinders, and measure and compare their volumes.