I've been taking one class at a time for the last six years at what I think is an average American university. The twenty somethings that your comment is aimed

I've been taking one class at a time for the last six years at what I think is an average American university. The twenty somethings that your comment is aimed at have been my lab partners and such. You're describing maybe 10% of them. As a group they're all over the map. As learning goes, I'd say anybody taking more than two classes at a time is overcommitted. They might manage to get A's but I speak with these students about the courses we took together a year or two after the fact and it's clear to me that taking four or five classes at once is an awful strategy for retention.