It's actually the first time if you never had to try before.
I think this is an issue that lots of people having an easy time in HS have, we actually need to learn how to study once things get more complex.
I actually don't think I was ever "naturally intelligent". My current grades prove that. But the reason I could cruise through high school was because my parents drilled me with algebra, vocabulary quizzes, geography, and Montessori school when I was 4-9 years old. That undeniably put me ahead for the next ten or so years.