I remember exactly my first time learning to code as a kid, the book I used used the "box" analogy for variables and it worked well. It was fairly uneventful experience, I just worked through the exercises at my own pace and was through the book in a couple of weeks.

The problem with learning to program in a classroom environment is that one kid may find exercise one difficult, another kid may find exercise three difficult, etc, the probability that any kid will get 'left behind' at some point is high. Classrooms are pretty bad places for learning.