Officer kite is pretty much spot on.
In my time I saw several people that were let go during training at all stages, sometimes for as little as 5 extra hours pre solo, or a few bad sims. Similarly people reached the end of training on the ATPL scheme and were told they were not eligible for certain airlines due to performance/scores.
I am fairly certain that figures of employment rates only include those that finished training with scores/performance above a certain level (allowing eligibility for all airlines) and that successful employment could include you going on to work as a flight instructor having paid for you own rating post training.
People need to be aware that nothing is guaranteed and that the schools are indeed businesses that are very well marketed. Once you are in you are just a number that can either gain the company money if you reach a certain standard that they can then sell on to an airline or be expelled, left or dropped if not.