Well, we've been "on top" of our son's education and development since he was a few months old really. Lots of quality time spent with him, playing, talking to him, going for walks and pointing out animals, birds, plants, standing at the bottom of our road "counting" cars, and tallying car colours, etc., taking him to feed the ducks regularly, reading at bed time, just lots and lots of "engagement" before he started school. Eg, he knew the alphabet, numbers, counting, colours, how to write, basic sums, etc. We'd never just sit him in front of the TV or give him a tablet or phone to play on to pass the time - yes, we watched TV, but we'd watch together and either DH or I would be talking to him, explaining things, etc. Most importantly, we think, is that we talked to him like an adult, no "childish" words etc once he'd stopped being a "blob" after a few months old - we'd speak "properly" to him, explain things to him, etc.
Once he was at school, we remained highly engaged, ensured he did any homework, kept on top of what he was being taught and made sure he wasn't getting behind. If there was no school homework, we'd do something ourselves to work through, all alongside normal "play" according to his age at the time. He was pretty quickly into computer games, and played an awful lot of online Lego games, Minecraft, Club Penguin, etc - all the kind of games where you build things, do tasks/challenges, move up levels of difficulty etc.
For the 11+, we didn't get a tutor, we just got 11+ study/revision books and worked through them with him, more to get him used to question style really, he'd maybe do a section of maths questions or a comprehension every few days for the Summer before the exam in September.
Once he was at grammar school, we kept up the same engagement with his schooling, i.e. checked his homework diary and kept him motivated to do homework, revise for tests, etc., and generally ensure he kept himself organised and on top of the work. As the years passed, we left it to him more and more, and by GCSE and sixth form years, we had virtually no involvement at all with his school work, just generic "have you done all your homework" comments in the evening, but we weren't really engaged at all with his school work - we left him to it. Despite excellent GCSE and A level grades, he never won a single school prize, as he was more of a "generalist", i.e. in the top 5-10 of each class rather than top of the class, so an all rounder rather than brilliant at any particular subject.
He's now in his last few weeks at Uni and on track for a first degree, but obviously, we're now "hands off" since he's been at Uni, so he is motivating and organising himself (we assume).
Both DH and myself really struggled at school for different reasons and both seriously underperformed, both leaving at 16 with virtually no qualifications, and having to drag ourselves back up to get self taught qualifications and decent professions. We didn't want that to happen to DS, so we were on top of his education and development from the earliest possible moments really. I wouldn't say he was an Einstein nor a Hawkins, so not a "high achiever" or any kind of "genius" in that sense, but he's got an excellent set of qualifications and an excellent job starting in Summer so he's got himself in a good place! Alongside that, he's popular and has lots of friends.