Different children need different tactics, though, don't they? Plus the whole educational climate is different nowadays - all sorts of factors determine which is the best approach for each child. Not least is sheer luck!
I hardly helped my first two, born in the late seventies. One was self-motivated and worked very hard, pitting herself against a clique of intelligent, highly-motivated girls all the way through school, had a series of really good teachers. Got good results. Went to uni, got good job, very happy.
The other hardly worked at all, had a lot of mediocre teachers (at the same school - local comp) who had to deal with a couple of challenging individuals in his class, and no friends who were at all interested in school. Got good results for GCSE but left school before A levels after not attending. Even so he went on to university, got a 2:2; spent a year sulking about how foolish he had been - and then got a brilliant job on a starting salary that was higher than mine.
Also there were several huge upheavals in their lives right at the time that my daughter was doing her A levels and my son was doing his GCSEs (deaths and births). But they still both got good results in those exams.
So when I look back I'm not sure whether my lack of input had anything to do with anything - although I still feel guilty for not having been fully focussed on them.
My last child (are you still reading, or have you gone off to make a cup of tea?), born in the mid-nineties, is having more problems than anyone else, despite being just as intelligent. He goes to a state school that regularly tops the league tables in our area, but he is very quiet in class, and no-one picked up on the difficulties he was having (high anxiety, mking it difficult to focus). I feel he has been very let down by some poor teaching and educational cuts which have meant fewer specialist teachers and several upheavals. He's the only one at home now, and I have been very much on his case, but sporadically, and ineffectually, as I have said above. He's not going to do anywhere near as well in his Highers as he could, and there's only a 50% chance of him passing, in my opinion. In his case, my attention does not seem to have made any difference.
But the hope I cling to is that this is not his last chance! As other posters have said, people often come into their own at uni (or afterwards, in the case of son No 1 above).
The problem is getting into uni, though isn't it...?