This activity should be completed before introducing the concept of standard deviation.
Have a discussion with your class about the color of m&ms found in individual bags. Is there a certain rule that's followed? Are the colors distributed by chance? Would you be happy if you received a bag full of ALL brown m&ms? Or just yellow and orange m&ms? Would that even happen?
The expected percentages (taken from the m&m website) are included in the document.
Once the discussion is complete, split the class into groups. Each group should receive one pack of m&ms. They should count the total number and the total of each color and complete the table.
Once each group is finished, combine the group data to form the class data table. Discuss the results. Are they close to the "expected" results?
Use the results to introduce standard deviation!