I've also taught, for over 30 years, although in a higher education rather than school context.Let's discuss pacing first since that was what your comment was about. I have taught for over 20 years. Lesson plans are almost identical to running a session.
I don't find the comparison between a lesson and a RPG session very apt. When I take a lesson, there is a certain amount of material that I have to get through, in order to deliver the prescribed curriculum within the timeframe allocated (X hours per less, Y lessons per week, Z weeks per semester). Therefore, planning how I will get through it, making room for dealing with student questions, handling student questions during the course of the lesson, etc are all important factors.
But a RPG session is not like that at all! As a GM, I'm not in a didactic relationship to the players at all. There's not some pre-established content that I "have" to get through. I look to the game system itself, and the unfolding events of play - and the way the former handles the latter - to ensure pacing.
If the game system doesn't reliably produce good pacing when played according to its rules and procedures, I would say that's an issue with the game. Which is not to say that different people can't have different experiences with the same game - there's nothing wrong with that! (In a recent conversation with someone playing Mythic Bastionland, I discovered that my group got through much more content in our fist session than their group does in a typical session.) But when it is in my table's hands, I want the game to produce pacing that works for my table.

