When the teachers are sitting in front of the students at the beginning of the school year Mr. D has on red shoes. Then the next time you see him in the classroom he has on brown shoes. You can see them when he is sitting in the chair in the center of the circle.
Mr. D is using a microwave to heat up a Moon Pie. In one shot, his left hand is holding the microwave door open; then we switch to another shot where the door is closed and he presses the following buttons: 1, 5, START. The next shot is a continuation of the first, where we see him holding the microwave door open. Also, depending on which shot you want to use for when the microwave actually started, it runs for either 7 or 9 seconds, not 15.
In Mr.D's classroom the Maryland flag is hanging on the wall upside down.
During the opening credits, when the camera is scanning down along the past Teacher of the Year winners, Stormin' Norman's' 1973 award is above his 1972. It is unlikely that when mounting these plaques, someone would skip a space and leave it blank for the following year.