There are a number of airlines that use the DLR for pilot selection, not just Lufthansa. The aim is to select the most suitable guys/girls according to a well defined profile on which extensive research has been conducted. It is not a question of finding the pilot with the best flying skills, the highest IQ, the best reaction times, the best grades in high school or the one with the most experience and things like that. It is about the people who offer the best all-rounder characteristics required from an airline pilot. It is about finding the potential/ability to perform and deliver without major deviation from a defined profile. The criteria established are based on a wide range of figures (a lot of statistics involved) and research done on thousands and thousands of people.
Because of the mean values used and ranges applied, one will find that there is actually very little one can do to prepare for the tests other than to go through the material the DLR supply for preparation. They test very stable traits within the personality of any given individual.
Like I mentioned before, only 8-9% of people pass the test. Because of the difficulty of the test, differences in terms of aptitude/potential between a pilot and a guy who has no experience whatsoever in aviation will be minimal if they both pass the test. The only difference between the 2 is that the pilot is some way ahead towards realising his potential whilst the other one has everything to do!
Once through selection, it is upto the individual and the company to make sure the conditions are favourable for the individual to achieve the said potential. Quality of training, quality of life are the factors that determine the outcome.
I hope it makes sense..!