Weed out meaning courses. Certain courses are unfortunately set up so that some kids just can’t hack it and they wind up changing majors or at some schools they don’t meet the requirements to declare the major. You usually can’t graduate from a program without a minimal grade in each class in your major. I wasn’t replying to her question in terms of applying to the major at a later date but more so as staying in the major period which she referenced by “weed out classes”.
Purdue is mainly an engineering school so if someone isn’t prepared for the Engineering Calculus, Physics, etc they are in those courses with Engineering majors who will be setting the curve. CS at Purdue is not in Engineering, it is in it’s own school, so those courses may be especially hard for those students. It’s also a very competitive major there so hard to say if he meets the criteria to get in or not or what his background is. This year is a crazy year in any case so anything goes really. Hopefully he applied EA there because they do say for CS there that is the best chance for someone to get in.