My son if 5 and was just diagnosed with ADHD along with some other things, so trying to put myself in your shoes regarding my own child is an interesting concept.. Not exactly sure what my own decision would be in a few years.
However, when i was 11 years old a group of my friends were sexually assaulted over a weekend for a birthday sleepover;i had not gone bu my best friends and girls i cared about were deeply effected.It was a long process,full of court,ptsd,and years of healing.My point being that the mature content i had questions and concerns about did not come from a book, but my own life and the people I loved. Knowledge is power and i also agree that your son will take what he wanta from the book his class is engaging in together. Sexual health is one thing always, but protection and healthy conversations about about boundaries as well as how we conduct ourselves and treat others is also an important conversation.
My ex husband dx with ADHD at a young age, sufferes from alcoholism, addiction, and anger which resulted in him doing 6 years in prison. My goal with my son/children is to have age appropriate conversations about life. The world. They dont need to know specifics about everyone we know, but mature content sadly is a part of our daily/worldly lives and can effect us all. Its ok to be protective of your son but aware and honest too. Good luck mama!