I never studied in high school. I also never did homework so I got a 0 for all homework assignments, then I just aced all of my test to finish with a low B average.
Then I went to Nuclear Power School straight out of High School. We were in class 12 hours a day 5 days a week. I never studied outside of class, even though the majority of people did 30-40 hours of study time outside of class (it was all logged and was mandatory for 50+% of the class because of the high standards). I graduated in the top 5% of my class with honors.
Granted, my IQ is much higher than average. But I have found that if you focus in class, take good notes, and don't get distracted it goes a long way. Most people just do not focus 100% in class. It is not the same for everyone, but make sure you completely focus in class and do not get distracted at all. Also if you have any study hall time or anything like that, use that opportunity to do homework or review material while it is fresh in your mind. If you review things while they are still fresh it helps a lot in memory retention!!!