The California 4th Grade Mission Project has been a part of the curriculum in many Californian public schools for quite some time. I'm not really sure when this tradition started, since I don't remember anyone doing this when I was in 4th grade, but it is certainly something I've been aware of since my kids started going to school.
Anyway, my daughter asked me to help her make a model of Mission San Miguel, so I blew up some drawings of the mission to approximately 1/72 scale, and used them as a template to cut out parts in cardboard and Styrofoam for her to paint and assemble.
The friars are made of regular modeling clay, and the sheep and cow are from a set of farm animals.
When I helped my daughter deliver the mission to school this morning, I saw that other kids seemed to use more manageable scales like 1/250 or so, but 1/72 looks much more impressive in comparison, and there's the bonus of being able to use it in gaming.
Still, the footprint of Mission San Miguel is already so huge that I think I'm just going to give up on the scale model of Mission San Gabriel Arcángel that I had wanted to build at one time.