Below are links to video for relaxing and basic exercises for students and adults:

I am not promoting these sites or videos they are free on the internet, helpful and different techniques for relaxing.

Breathing and slow movements you could do in a room or outside.

Breathing exercises with Gentle Qi Gong Exercises  seen on PBS (7 minutes long)

Another exercises video on breathing and slow movements by same group above video (7min)

Qi Gong - Breathing (2 min)

For adults to view first and determine if this would be good for your students depending on age.  

Stiff Neck and upper back

Qi Gong for Upper Back and Neck Pain slow movements (Video)

Qigong Chi Kung Fundamentals for Beginners (3 min)