The Helium stick is a deceptively simple team-building activity that is fun while encouraging your group to problem-solve and work together in community.
All you need is a long, thin dowel rod. Line the group up in two facing rows, each person holding out their arms with their index fingers extended. Lay the "helium stick" across their fingers and have the group adjust their arms until the stick is completely horizontal. The task: to lower the helium stick to the ground while keeping every team member's finger in contact with the stick at all times. Grabbing the stick in any way is not allowed. It must simply rest on the tops of their fingers. You act as judge. If at any time the stick ceases to be in contact with any person's finger, the challenge starts over.
Strangely, as the group works to lower the stick, one end or the other will have a tendency to start rising, hence the name of this game. If the group seems to be achieving their goal too quickly, make sure they are following the "all fingers in contact with the stick" rule strictly, challenge them to do it with each person holding out just one arm, and make certain they actually get the stick all the way to the ground. If the group is getting frustrated with a lack of success, encourage them to take a breather and work out a plan of attack.
For more back-to-school ideas see here and here.