Really weak students can do exceptionally well in Scheme. For the second year in a row, at the beginning of the school year, I found that a weak student signed up for my class. And as I did the year before, thought to myself... "this kid may not make it". Last year, the student struggled and at mid year I was hoping he would drop, I even talked to the guidance counselor about it. One thing that helped this student was that he was teachable... he followed the design recipe religiously but couldn't get his programs to work. Sometime in the second semester as things got more difficult, he started to do better. Things started to click. And he made the 2nd highest grade on the final! Most importantly, he had gained a whole lot of confidence.
This year, I have another student like that... (you'd think I would know better than to assume he would do poorly) and here we are at the end of the year, and he is doing just fine! I'm very proud of him, and again, he's pretty proud of the progress he has made.
My point is... before I started teaching Scheme, weak students would get overwhelmed by it all and would start a downward spiral. With Scheme, if they just keep plugging along, weak students will have a strong finish. And that's a great feeling for both of us!