Welcome to the supporters side. I have a 20 -17-15 year old in my home. I have a great relationship with my children. My advice would be, work on having open communication. Let them make their own mistakes ( unless you know the mistakes would have heavy consequences) making mistakes and learning from them is how they grow as a person. Be honest with them, share some of your own life experiences with them. Let him/her see your human.
Help them try new things and hopefully they will find a new interest or hobbies. Listen to them when they talk and hear what they are saying. A counsellor once told me, you have to let your children experience their own life and experiences. Sometimes we think we know how their going to feel about something because we were a teen once. But the truth is, we all have our own feelings and we all see life, situations differently. Let them experience their own. Let them know you will always stand by them and allow them to be who they truly are. Teach them they have a voice and that voice can give them strength. Let them be a teen, Society pushes them to grow up to fast. As we all know your only a child or a teen for a short time and an adult for much much longer. If he/she struggles in school, let them know your there to help and support them. Let them know they have a voice to express their needs.
You have a voice also. You have a right to do what’s best for the teen your supporting, not what best for the school. Most of all validate his/her feelings, you don’t have to understand or agree with them, but they belong to that person. Let them express their feelings, weather it’s anger, sadness, happiness, fear. Just teach them positive coping skills. I’m sure I could go on and on. But then I would be writing a book, lol. Hope some of this helps.