I've never seen a US-based system that weights classes later in the curriculum higher than the beginning ones (which is too bad, since like many, mine rose towards the end).
Swarthmore has a system (the Honors program) where the degree granted (graduation, with Honors, with High Honors, or with Highest Honors) is based on the judgement of external examiners on the quality of examinations (written and oral) taken at the end of the senior year.
