The single biggest difference between high school and college is that college is much, MUCH more open ended than high school.
While most colleges have a set of classes that you must take, the majority of classes you take are up to you.
Additionally, your days are not nearly as structured as they were in high school. There are oftentimes long breaks in between classes where you can do whatever you want. You are not stuck in one building for seven hours for five straight days.
Because your hand is not held throughout your college years, fewer people actually care about your success. Unlike high school, the administration could care less about your grades so long as you keep sending them a paycheck. Classes are usually so large and their tasks so many that most professors will not proactively help you out.
In order to get people to help you out, you must go to them in college. This might irritate some of you, but it is the cold, hard truth.
In general, college classes are not more difficult than high school classes. While they might seem harder at first, the truth is that they simply require a different skillset.
College students who are not getting the grades were unable to adapt and work on that skillset.
Socially, status and popularity are less important. You can build a social circle with as many cool people as you want regardless of what you do.
While it is still possible to become popular in the “social scene,” not having that popularity is no barrier to making friends.
Things that were kept underground in high school like alcohol and drugs are out in the open in college (so long as the cops aren’t around, of course). If you are into those things, you will have no problem getting them in college.
A final point is that college students are more mature than high school students, so sex is pretty normal amongst couples. It is not uncommon for condoms and lube to be passed out to promote organizations and events.
Obviously, this wasn’t the case in most high schools.