College courses are commonly seen as harder because:
- Faster pace.
- More advanced material.
- Higher assumed level of student ability.
- Less supervision, so students need to self motivate and do their own time management.
- More in depth assignments and projects.
- Grading spreads students who had 3.6 to 4.0 high school GPA over the 2.0 to 4.0 GPA range in college.
But there may be some easier aspects:
- Less busy work.
- More choices in courses to choose those of most interest to the student.