Basically, the kids play drums on their chairs. Yup. That's it.
Then, you are given non-traditional notation - measures with pictures of the drum pieces, showing which are played on which beats. The files you get with MFI include cool rock favourites with the drums simplified and yet varied for the different sections of the song. It's harder than your typical, basic rock beat; it's much easier than intermediate drumming. Like Goldilocks and the Three Bears, it's just right!

Here is an example from a workshop in Cyprus (you'll need a VPN, my China-based friends!) This is a teacher's workshop; however, when I was in Hong Kong, they had a grade 5 class learn this for the first time, and the kids picked it up really well.
a) It's cheap and so you can get an entire class drumming immediately
b) It takes away the prestige of the drum set, in which only a few chosen kids get to play it.
c) It gives the basic skills on drum set, so when the kids get into their creative cycle groups and start deciding on instruments, everybody in the group can already play
d) It's a great gateway to playing on a real set. It's a way of talking about proper hand positions, etc., before they get on a real kit
I should say, thought, that standing isn't very helpful. When we learned this in the workshop, the teachers all sat down. This was better because it was more comfortable, but also because it more closely mimicked a real drum set. (Drummers don't typically stand when they play a kit!)
I'm in the middle of the creative cycle right now, so it's too late to introduce this to my classes. However, next semester's grade 6s are definitely all going to try this. I'm excited and am getting ready NOW!