The criterion for acceptance into the school is the willingness to put in the effort to achieve full potential, not high 'innate' ability. Placement into classes is determined by academic attainment, with age acting as a limiting factor. Students applying to enter any class in the school must take diagnostic tests to determine placement.
Students who are found to be behind academically are not refused but rather given the chance sometimes at an extra cost, this is one of several different solutions, depending on the nature of their academic problems. They may be:

1 - Summer school: A six-week summer course offered in June, July and August. Students who are academically below the required standard can attend this course and by doing so may avoid losing a whole academic year. 
2 - Special lessons: A student found to be weak in one or more subjects attends extra periods in that subject until the level of the class is reached.
3 - The full-special classes: Students are given accelerated programs intended to prepare them to join the regular classes. In many cases, full-special students have done the work of two or more scholastic years in one.