Depends on the school. All of my math classes and most of my CS classes at purdue were bell curved around like a C+/B- and you had to get a C to pass the class. Thus, a portion of each class would not pass and be effectively forced to retake the class to learn it better or switch to an easier major.

What schools do you have experience with? Also, never heard of ACM so I have no idea if that was used whatsoever for our classes.