My experience with the school pix was with an outfit named Bell Foto Labs. Had schools in a 100-mile radius from the lab. The schools were everything from the "one-room school house" in rural PA/WV/OH to K-12 with 700 heads a day. Quite the experience. With the larger schools, there was no room for deviation if you were to stay on schedule!"Line 'em up, smallest to tallest!"
Learned I had to be a bit of a clown, too.