There are certainly kids in my school whom I discipline differently because I can discern regret, remorse, repentance, etc., and I know they've 'learned' just by our conversation. Other students, though, seem undaunted by even the prospect of 3-hour Friday detention after school.
For the sake of fairness (and not wanting to have to deal with the parents who'd cry foul), the easiest route is to implement completely even discipline--zero tolerance.
Also, though, what do you think the coverage would be like if the school had given a 'light' punishment to a student who then goes out and makes real trouble after being 'let off' by the school? This is why risk-management (i.e., lawsuit avoidance) is so powerful an idea (and dept.) in school and society
I don't like zero tolerance, but the schools (indeed, public agencies generally) are in a tough spot either way. Imagine trying to implement a 'some tolerance' policy, especially in an environment of low trust, as people now generally have for the schools.