There was an article here a month about this (related to an art program IIRC). Basically a number of schools "entry level" courses for certain majors aren't passable by someone with a general high school degree because they only accept students who already learned the groundwork before applying to the program.

I noticed this recently while looking at MIT's computer science program for a data structures class I could recommend to a family member.

Apparently MIT doesn't have an intro to data structures class. The I guess the assumption is that everyone applying to the program got their linked list/searching/sorting knowledge before beginning the program. They have a number of algorithm/datastructures classes but none of them teach the basic concepts. Similarly. I don't think they have an algebra I class (they have one called that, but its not what one learns in HS algebra, has calc/etc as prereqs). That might make sense because the basics of algebra are fairly consistent across HS curriculum and everyone takes it, but comp sci/data structures classes are all over the place, and I can see situations where a subset of students is scrambling to understand pointer linking/etc in the intro to algorithms class they have someone outside of the major taking their into to CS classes.

So, I haven't applied to MIT (lol). But some schools I applied to did ask what major I'd like to do. It could be that MIT doesn't accept applicants who want to do CS who haven't taken some level of CS fundamentals before.

My school wasn't that mean. I think the programming II class was the weed class, and I think the deciding factor was that the projects just took a lot more time than homework you're likely to get in other 100 level courses. I had no CS background but with enough time I got through the homework. Not everyone had the time or the interest.