You could ask your school friends about things that are going on in their lives and let them know you’re praying for them. You may never know the effect this may have on your friends. Although they may not believe in the power of prayer the fact that they know someone is there who cares can make a huge difference!
Ask them a week later about how things are going. Even if there’s no difference in their situation, let them know that you will continue to pray, and that they can come talk to you about any other issue they might like prayer for.