Misconceptions about core linguistic concepts like mutable variables, mutable compound data, and their interaction with scope and higher-order functions seem to be widespread. But how do we detect them given that experts have blind spots and may not realize the myriad ways in which students can misunderstand programs? Furthermore, once identified, what can we do to correct them?

In this paper we present a curated list of misconceptions, and an instrument to detect them. These are distilled from student work over several years and match and extend prior research. We also present an automated, self-guided tutoring system. The tutor builds on strategies in the education literature and is explicitly designed around identifying and correcting misconceptions.

We have tested the tutor in multiple settings. Our data consistently show that (a) the misconceptions we tackle are widespread, and (b) the tutor appears to improve understanding.