Tom always got stuck at the same place and no matter how much he practised, he always made a mistake there and stopped. He had done that long enough and was in fact practising a mistake.
I advised him that in some cases it may be practical to change the strategy and try to practise in a different way. By always starting at the beginning of a section and stopping at a certain place it was not possible to practise the end part very well. Tom never got there.
Sacrificing fluency and rhythm in order to have all the notes right is a behaviour students should really try to avoid. For that reason I asked him to work back to front. Start with the last bar of the difficult section.
A good example is Christopher Norton's 'Tram Stop' from Micro jazz Collection nr. 1. The first four bars are Ok, but then students have a real problem with the following three bars:
Start repeating the last bar until the reposition and drop of your left hand is fluent and easy.
Then you go 1 bar backwards and start with the left hand there. It is important not the stop at the bar-line. A bar-line has no musical merit whatsoever. Music always wants to move over the barline towards the first beat of the next bar!
Then you add the right hand of that bar.
Then you start one bar backwards again. And within a short time span Tom was able to play the whole section fluently.