The first problem is the notion of absolute precision and detail required to do even the simplest task. The next is how syntax relates to such notions. Then comes mapping the syntax to the task. If they don't grok variables at this point, they're not going anywhere. A lot don't. Above all is the imperative of completion: if they don't make it work somehow, it doesn't work period. I'll try to salvage their work, tell them what to fix, and accept resubmissions - but if it doesn't work, it inherently won't pass the low bar for success.