From my own experience, the senior year (including the summer following graduation) is the time to help your teen make the transition from dependent high school student to independent college student with a few simple changes.
First, stop keeping their calendar, handling their money and doing their laundry; these are life skills the majority of 16- to 18-year-olds can — and should — handle themselves. Have them call the doctor and make other appointments; they'll need to know how to negotiate the student health center if they get sick at school.
Set them up with their own banking accounts and review the fine art of balancing a checkbook with them. If you're still doing their laundry for family efficiency sake, don't wait until the last minute to explain the importance of separating lights and darks lest their first load of wash in the dorms turns an odd color of gray.
And, if you're the parent of a soon-to-be high school senior, fight the desire to constantly check their grades on their school portal. They can — and should — be able to manage their assignments by now.
Second, make sure your 24/7 connected-teen understands that technology is not fail-proof. Ignore their rolling eyes as you calmly explain that email systems can go down, so they shouldn't rely on sending a paper, at the last minute, to their professor (or high school teacher). Remind them that computers, including the handy phone device they use more for texting than talking can get lost, stolen, broken or just plain quit working.