If I were the teacher of a high school class, I would in fact consider seating my students by grade. However, I am currently a student, and I would be angry/jealous of my fellow classmates up front. So, if I were a teacher, I would seat my students like this: If the date was May 6th, number 5 and number 6 will sit occurding to the day. Let's say it was a Monday. Monday is the 1rst or 2nd day of the week, depending if you count Sunday. I don't. So, 6 and 5 will sit in front. Since it's 1. After that, 7,8 in the second row 9,10 in the third, and so on. If the row is full, move on to the next line, and count on it. This will work at anytime.

Also, once a month, i'll let my students sit where they want. Although I'll never become a teacher, let's say I will tell this to my future high school teacher.