Use a spacer. The best way for a child who needs help with an inhaler, is to use a spacer. That is a bag or cylinder which the spray is released into, then the child puts the mouthpiece in the mouth and just breathes in and holds breath for about 10 seconds. It is important to teach him how to do this at home.
Video. There are two separate issues at hand. One is to acquaint the school staff to signs and symptoms of asthma, and the second one is how to physicaly use and inhaler and a spacer. Talk to your school nurse so she can provide an in service to the staff. If this is not possible you can ask your doc to do this for you. If you just need to teach mdi use, go to youtube there are great videos on this.