Teen returning to school after rehab

My 16 year old went to a 60 day rehab program back in November. He got addicted to narcotics. And was doing them behind my back from almost a year behind my back after he got prescribed narcs when he was in the hospital for a bad kidney infection. When I found out he was doing drugs I put him in therapy but then the narcs shifted to meth and fentanyl and he started to self harm. When I found out he was doing meth and fentanyl it was when the school called me because he was being sent to the hospital because he overdosed in the bathroom. We went straight to rehab after that. Everyone at the school knows he went to rehab because of the overdose. He came back home last week and I gave him the week off of school. His best friend has came by everyday to hang out after school. I guess what I want advice on is how to make his transition back to school as easy as possible. He goes back Monday and I know he's nervous and embarrassed. Any advice from people who have experience with addiction would be appreciated. But any advice will do as long as it's positive will do