From my experience the middling ones are exactly the students who have the highest cost/benefit ratio. The checked out ones are the students who could have a small amount of attention to get them over a hurdle that’s completely blocking them, which caused them to check out. Maybe you find out they are dyslexic. Or you find out they are not eating breakfast or lunch after a short conversation. Or you find out they’re checked out because they’re bullied. A small change here can yield a drastic improvement.
The middling ones are usually performing at their highest cylinder and still not doing great, so it takes a lot of work to convince them to apply themselves even more.
TLDR; it’s easier to get a student from F to C than from C to A.