I've been using it for 2 seasons now with Leeds, and i didn't really get any progress until about halfway through the second season, when some of my younger first team players starting coming on strong and improving considerably (Delph in particular).
I found that the key was using your coaches efficiently - I completely changed my coaching staff and now have 8 coaches that are being used for their 2 highest attributes, some doing 1 assignment and some doing 2 assignments. The coaches workloads are all light, and the training is between 5 and 7 stars.