This estimation and data jar is perfect for grades 2-6. Use this form (and customize it to fit your needs) to place on a jar. Students can take the jar home, fill it with inexpensive goods, and bring it back. Then in class, students will guess how many items are in the jar. At the end of the week, the student who guesses closest should receive a reward. I give out candy, but you can do whatever you want.
With younger grades, the estimation jar works wonders helping students learn to estimate!
When you are working with older students, the jar changes to the estimation and data jar. After each student estimates, compile all of the estimates. Then, find the mean, median, mode, and range of the data. This is a fun, educational math activity that promotes estimation and data skills.