Fair anecdote. I'll offer that in my experience teaching hundreds of students, most don't have trouble with the cascade from locals to globals to builtins, and

Fair anecdote. I'll offer that in my experience teaching hundreds of students, most don't have trouble with the cascade from locals to globals to builtins, and quickly grasp that globals are looked up for each call. That closures work at all confuses the ones who are thinking carefully about local scope. I may have a biased sample of students, but I think it's decent evidence.