A class of 200 students performing much worse than the last class is very unlikely. 200 Students is enough to make even small differences statistically significant.
A single test being much harder than the last test is much more likely, since it isn't an averahe of 200, it's a single datapoint.
That's why if this semester's class performed much worse than last semester's, you can assume it's because of the test, not the students.
Unfortunately, GTK is much prettier than QT.