" I've gotta try harder at school."
It sounds like study hard at school to me. When googling it, I found try harder, try hard and trying hard. Do they have same meaning? I'm guessing:
(1) try harder is a comparative form
According to Urban dictionary:
someone who tries way to hard and spends too much time to be good at something that is pointless
(2) try hard is an original word
A person usually of little talent who tries hard, especially through imitation, to succeed, usually to gain fame or popularity.
(3) trying hard is a gerund. No. 3 definition by Urban dictionary:
a person who struggles to achieve something but he/she is hopelessly doing it in other words, they won't be able to do their task whatever they do