- Assignment Outlines - that paper/PDF you get for your assignment would be horribly vague. The only way to get a clear idea of what the professor wants is to go and ask. Unfortunately when you do that, the answers are also fairly vague, so in the end you'll have to try and guess what they want. (In retrospect, this one actually does happen in university sometimes. I'm leaving it here since in real life this is the norm, not the exception.)
- Assignment Requirements - at some point before the assignment is due, the professor will change what the assignment is about completely. You can either adapt what you have, or start it again from the beginning (although most students procrastinate so it's likely that they won't have anything yet).
- Assignment Review - after showing the professor your assignment, they'll change their mind on what they want. Unlike the previous point, this will only occur after you've shown them the assignment, which heavily penalizes procrastinators.
- Grading - there won't really be any grades in the same sense of the word. Some assignments will have some crazy weighting system, so if you get 90% if the answers right you'll still fail, but your friend who got 20% of them gets a good grade since s/he knew exactly which ones to do. Unfortunately you probably won't figure out this weighting scheme.
Another possibility is that the grading system is either 0 or 100. The professor doesn't care if you've got the features 90% built, they want to see everything that they asked for.
Other assignments won't have a grade at all, instead the professor will just accept what you give. 6 months down the road if the assignment was poorly done, you'll be kicked out of university; if it was well done nothing will happen. (An explanation of this one: many times in the real world you're asked to make a judgment call, and the client will just accept your conclusion. After all, you're supposed to be the expert. However after a certain amount of time, evidence might show whether that was a poor decision or not.)
- Competition - your friend does a good job on the assignment and hands it in a week ahead of you. You fail the assignment, regardless of how good it is.
- Other people's work - instead of you starting the assignment from scratch, you'll get the version from last year's class and be told to change it. (it's possible that some professors already do this, which is a good thing!)
- New technologies - you'll start new courses that need you to use a specific programming language or technology that you may or may not have done before. If you don't learn this technology within a few weeks, you fail the course. (there are a few courses like this, especially if you go to a school that teaches Java in first year and then drops C on you at a higher level - this is a good thing!)
A little side note: I am not suggesting that computer science programs change in order to create better programmers. A computer science program is not about teaching people how to be better programmers, it is about teaching people computer science. While I do think computer science is a good discipline to study if you want to be a programmer, the actual becoming a good programmer part is your responsibility.