Depending on the class and professor there can be A LOT of tests. I had seven tests plus a final exam in one class. Regardless of the amount of exams, the professors assign a lot of reading per each exam. The books also have longer chapters, smaller print, lots of information, etc. Then take that and add 4 or 5 more classes to it. It takes a lot of energy, but as long as you keep up in the class, it isn't as hard. It is just challenging.
The other thing is that in high school, teachers were more helpful because it was a smaller school community. Some professors I've seen don't put too much energy into helping their students. I've gotten marked down on papers just because the professor didn't like my writing style. But don't let that scare you. There are a lot of profs. who ENJOY helping their students. Just keep up with reading and assignments, go to class, and keep in contact with professors if you need to. You should be fine.
Then it was found out you STOLE that from Yahoo Answers
