All the credit to the idea behind the Hexagon Task goes to James Schaffer. The Hexagon task works on establishing students' understanding of arc length and sector area. It is a student lead discovery that takes some time and patience but really leads to a solid understanding and development of the formulas.

Here is the task (gsp file).

Here is the warm up.

Here is the handout.

Here is the lesson plan.

Here is the homework.