He's quite right.

My son would have the same problem, and probably for the same reason. If she actually said "focus on the concepts being taught", then the problem is that she wants him to think about the big picture of the bartering system, and he is thinking about the details of what she is teaching, which is the iPhone. He perfectly well thinks he's paying attention to the teaching, but she's on another page altogether!

She should definitely know this by this point in the school year.