I've read the thread about motivating teenagers with interest.
I can only give anecdotal examples but I've made a few observations over the years about the parents that have incredibly committed children who studied hard and those that don't. Broadly if good habits are instilled when the children are young I believe you are less likely to have a problem later on. Writing it down this seems blindingly obvious to me at least.
If you push too hard and have unrealistic expectations your children will probably rebel however if you've insisted on high standards, homework completed well before deadline etc when the children are very young the chances are they will have good study habits later in life.
Those I know with teenage boys in particular were very laid back about homework, deadlines etc. They gave no real support early on and made no demands. The boys were allowed to play computer games and outside with their friends, study outside of school not a priority.
When the boys turned 11 or 12 the parents tried to get them to work and the boys refused. Many very able boys got Cs or Ds in GCSEs when they were capable of far more. The parents shrugged and said 'what could we do? we tried everything'. It breaks my heart to think of a few young lads I know in dead end jobs when they had the ability to do far, far more. They may go on to do well in time of course.
I came from a 'fly by the seat of your pants' family. Library books were always lost, packed lunches made at the last minute with stale bread and yoghurt past its sell by date etc. Buses would be missed, I would arrive at school aged 6 in odd socks, you get the picture. No help on school projects etc. It meant I have stressed and felt that I was likely to fail somehow.
I am trying to instill calm in my family. To tell my son the rules are he does homework, spellings or project work immediately it's set. Library books have a special place, packed lunch is prepared in advance etc. So far so good. I am sure that I could have a rude awakening down the line but at least I am trying and I think these things DO make a difference.
When I look at those who have children who are self starters and have achieved high grades at GCSE etc even if not hugely 'bright' the parents have without exception had a great work ethic. They've modeled that work and life can be tough but setbacks can be overcome with a positive mindset. From the age that the first set work comes home there are no excuses, work assignments/homework/projects HAVE to be done and begun practically as soon as they are set.
There's usually been a love of learning promoted & encouraged from early on too. It also has to be said that great deal of time was invested in the children from an early age.
Something else I've observed in friends with 2 or 3 children, again just my own experience and not sure if it applies my broadly? With the first child the books were out on the table every Sunday, sometimes all day Sunday. The Mum was on the phone to her friend as they discussed science homework in depth. I was called at work to discuss grammar rules. The Mums seemed to assign 'mentors' in every subject for their DCs from when they were about 8 years old.
DC would end up at a grammar or highly selective school where there was a high % of A*s. Peer group hard working and driven etc.
With DC2 it was a different story. Mum was usually burnt out by then and found that she couldn't invest as heavily in their education. That child usually wasn't as 'academic' it turned out in the long run?