The schools are sponsored by the Government of the day, and attendance is mandatory.
Why? When, when kids could learn at home?
Two reasons
These days a kid could learn at home from free on line resources such as Wikipedia and Google Books, and there are are Stack Exchange sites for expert advice and opinion. However without a structured approach to material a student could easily miss the foundations of a subject and then be unable to comprehend - or worse think they understand - the more advanced portions of a subject. So structured learning is your first reason.
Secondly, in this cyberpunk society it's useful for citizens to have a similar frame of reference, speak similar languages and technologies and have a somewhat homogenized view of their society & world. However, given the level of tech in such a world, the prevalence of AI and targeted advertising, it's absolutely within the grasp of the ruling caste to take this one step further and ensure that that children are indoctrinated/brainwashed to not rebel/rock the boat/ask the wrong questions. School is used to brainwash a compliant populace.