There’s been a lot of great advice here. Just a couple of things I’ll chime in on:
Set clear expectations with your kid and get them to take charge of tackling these potential pitfalls. Discuss the possibility of coursework being more challenging and the likelihood that it will be much harder to skate by using smarts to make up for procrastination and disorganization than it has been in the past. Lay down your expectations and priorities - dipping grades due to tough grading is different than missing assignments, not doing readings, or unexcused absences. Are there conditions for staying at boarding school? Or behaviors that will cause you to get involved and ask for additional structure from the school? Be as upfront as you can while also expressing your confidence that he’s up to this new challenge.
Have a talk about specific worries. Both of you read through the student handbook in advance and then make a list of things that might be stumbling blocks. Let him go first and then you can add in as needed. For each item, write out action steps to head off issues. Ex. Potential issue: oversleeping and missing the first class or commitment of the day. Action steps: 1)Use an actual alarm clock, not his phone. 2) Ask his roommate or a hall mate to wake him up or bang on his door if they don’t see him moving by x time. Make this an ongoing collaborative process once the semester starts; if he misses a class or two, ask him what needs to change to keep it from happening again.
Second big point: schools have varying levels & forms of “scaffolding” to help new students gradually develop independence and responsibility, but most have additional structure that can be put in place for specific kids. Supervised study halls in the evening (outside of the dorm) or during free periods is a common example. Sessions with someone in the learning center (or equivalent) to go over things like setting up a study schedule/assignment calendar & following it, showing the advisor on duty in his dorm his homework/study plan for the evening and calendar for the next day at check-in every evening, handing in his electronics for a couple of hours a day or at night, scheduled meetings with teachers or a writing center to go over paper drafts (so he can’t wait until the last minute to start), etc. He can always blame it on his parents with an eye-roll when talking to friends, even if it’s something he initiated.