My parents were initially involved, especially at primary school, but seemed to lose interest when I went to secondary. I went from being a straight A student to failing all my GCE's except 1! They only attending my first couple of year's comp parents' evenings and by the time I was in 4th/5th year, I didn't even show them my reports (and they never asked).
It wasn't a matter of them not being interested, they were busy. Father running his own business, mother working full time during the day and also taught evening classes (yes she was a teacher which makes it more ridiculous!). It's not that I was ever troublesome - I never had a single detention or other punishment, not even lines! Behaviour wise I was a model child and pupil. I was just completely dis-associated with school. Serious bullying didn't help as that just made me withdrawn. I just turned up at 9am, did the bare minimum I could get away with in lessons and homework, hid at breaks and lunchtime to avoid bullying and went home at 3.30.
Had someone, whether a parent or teacher, given me a kick up the bum and some support, I'd have done a lot better. Because no-one else seemed to care, neither did I! You'd have thought that getting As in the first year at comp and slowing going down to Bs, Cs, Ds etc as each year passed would have flagged up a problem, but even with the same form time for all 5 years, he never once flagged up a problem, never took me aside for a chat, never queries why my parents never signed & returned the report slip, etc.
All changed once I left the horrid place and got a job. I took A levels, did evening and day release classes and eventually qualified as a chartered accountant. Leaving school was the start of my life! Do I feel let down by my parents and teachers? Yes, 100%. I managed to turn my life around but it was a close thing.
When I had a child, I resolved to be fully engaged and supportive in their education. So far, so good. He's a high achiever and things look good for him, but educationally and socially. He has loads of friends but also a A* student across the board. I'm not a helicopter parent, he's not stressed with studying at all. He knows I'm there for him. Most days he'll do his homework without my intervention. Some days he needs a nudge to get on with it. Some days, he'll struggle with something and ask for help. We were very hands-on with his work etc in years 7 and 8, but we eased off in year 9 and now more just supervisory in year 10, particularly as he's now gone beyond our abilities to help him!
So, yes, parental involvement is absolutely essential. But perhaps more a matter of showing interest and being there for your child, rather than doing their homework for them and interfering in every little thing going on in school. It's a fine balancing act I suppose.