I've found, with coming to college, that there are quite a few things that have changed quite a lot since high school. The college experience is completely different and here are a few reasons why:

You live on campus

No more school buses or having your parents drive you to school. Instead, you get up and walk to your classes and then go back to your dorm.

Class schedules

No more 8-a.m.'s! Well, maybe not--you can get them in college--but it's not usual. Sometimes you will have all your classes in one day; sometimes you'll have two; sometimes you'll have none; the schedule varies from each semester--unlike high school where it is the same routine every day.

Shorter year

College runs much slower than high school. A high school semester is about five months long, if you only have two semesters per year, while a college semester is only about three.

Mandatory vs. Voluntary

High school is mandatory and many students don't want to be there. College is voluntary and the people there, want to be there. Also, classes in high school are mandatory to go to, while college it is strongly suggested that you be there.

Deadlines

High schools usually have flexible deadlines to work with. If you miss an assignment, you usually have time to make it up. In college, the deadlines are very time sensitive, very few times will you be able to have extra time to get an assignment in. The deadline is the deadline.

Losers

In high school, those people who actually did all the work were laughed at and called nerds, dorks, losers, etc. But in college if someone doesn't do the work, then they are the loser.

Oh, and that whole social hierarchy in high school? Yeah that's gone. People in college get along pretty well no matter what “rank” they would have played in high school.

Bathroom breaks

Remember those hall passes from high school you needed to lug around to go to the bathroom? Those don't exist in college, no need to ask either, just get up quietly and go.

Rules

High school classrooms had a lot of rules. No food. Only water. On and on. College classrooms are laid back. I've seen so many students lug in a whole lunch and eat it right there in the classroom. You still have to respect the professor's rules, but those are few and far between.