At 8 years old, don’t worry about if his current behavior will continue as an adult — that’s too far off. Plus, ADHD is a developmental disorder, so he’s 2-3 years behind his age in skills and development. That means you’re parenting a 5-6 year old.
I would set up a reward system for this one goal of going to classes every day and not skipping Mondays. We have dealt with some serious school refusal with our son and writing up a behavior contract that includes a reward every time he attends school for 10 days straight without fussing or leaving early (a bonus amount on his allowance). It has helped.
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism