unless your english is really good, or else you will have a hard time catching up (at least inthe US)
for US high school (if u plan to go to a university)
you will need to have a good GPA (grade point average) meaning, every semester your grade will count
and u will also need to take SAT/SATII (or perhaps TOEFL)
and then do extra-curricular activities, etc.
if you`re not willing to study much harder, then i think it`s a waste of time/money to study aboard.
just my opinion^^