Hey
PoetVogonAll in all, this is a very good essay, probably a 5. It's sufficiently long (over 500 words), well structure (opening paragraph, 3 critical paragraphs, summary) and well written. Most importantly, it goes right to the heart of the matter, casting doubt on whether the correlation observed indeed implies causation, as assumed.
Small comments: 1) the first critical paragraph would be bolstered by an alternative explanation or example (as you do well in the next paragraph). You are correct to say that the correlation is insufficient to determine causation, but should back this up by pointing out an alternate reason to explain the correlation: an opposite causation (the computer instruction was introduced because the student cohort was very strong and it was thought they could handle it), a common cause (the computer instruction was introduced as part of a larger educational overhaul of the curriculum, which benefited students), and so on.
2) the first and second criticisms are really quite similar (the distinction between the reason for their declining dropout rates and success in college seems artificial). It would be better to have combined them, keep the third criticism (which is really quite different), and add another criticism, or alternately - devote a paragraph to dealing with counter arguments..