What went wrong?

As I was grading finals, I got to one that just befuddled me. Actually, the student has befuddled me all semester.  Mostly because, despite anything I said, wrote or explained (repeatedly) this student never seemed to understand the concept of critical thinking. Regurgitation was not a problem, but going beyond that was like pulling stumps with a soup spoon. Because the class was an advanced one, he was transferred to a regular english course for the next semester, so this final was the last hope of seeing a spark of understanding.

Granted, at the beginning of the semester there are a few students who have this problem. After a month, however, few are still confused. This student never got it. Not conferencing, notes, models, diagrams...  nothing seemed to phase this student. He just went on his bumbling way without any thought to anything I said, other students said or did. It was like trying to talk to rock.

On the final, the students were to read a prompt and passage and then write a thesis and outline for an essay. This student, once again, wrote a summary of the passage. Seriously, what the hell went wrong? This student was obviously left behind, because he got nothing out the semester. And I'm desperately trying to figure out what I could have done differently. Next week starts the new semester and there are others who are struggling to keep up; how do I ensure they aren't left behind either?