Explain to the participants that the objective is to get into a birthday line where they will be placed according to their birthday and month.
Add that they have certain limitations when carrying out this activity. The activity will be done without talking. It is also forbidden to show identification and to write.
Tell them that they will have three minutes to finish this activity and ask everyone who is sitting to gather quietly and form a line.
When the time is up, starting with the first person, ask each participant in turn for their birthday, month and year. Place the people in the wrong place in the right place with humorous comments.
How many groups do you want to divide into (say 3), count from one to 3 and ask people to keep the number in their minds by counting 1-2-3-1-2-3-... from the beginning to the end of the line.
Put all ones in one group, all twos in another group and all threes in another group. You now have 3 different working groups.