Having worked in the field of IIT JEE training for last 15 years, we realized the 'real game' of these so called prestigious coaching institutes. Have a look at the insider information.
The modus operandi is as follows. (Which we can also follow if our morals allow).
Advertisement Gimmick : Every 'big' institute advertises their last year results on big hoardings with many results (many results are genuine but quite a few top ones are 'purchased')
Typically on any big coaching institute, out of 80 in a batch on average (not those 'excel batches' but averaged on whole), selection of students is around 4-6, per batch!
On admission, students who are otherwise brilliant and score more than 95% and also score very well in admission tests, are given hefty discounts of about 90-100%! These students might get selected on their own or with any normal coaching .
Read a real life student account here