I got this idea from Pat Walsh. Start with a 10 by 10 grid and have the students color in the squares starting in the center, spiraling outward. Each number has a different color above. Have the students conduct a survey of something of interest to them. Favorite music, sport, school lunch -whatever.
Students then calculate the fraction of the total for each.
They convert it to decimal and multiply by 360 degrees and then create a circle graph of that data. Students enjoy this due to their personal decision of topic, the coloring aspect and the social nature of conducting a survey. Teachers like it due to the many skills that are used in it. Glue the triangles onto the tennis ball and calculate the surface area of it. The article has great pictures and references.