The guy's school puts up lists of students in each class using ids for each student so they can't be identified except by parents of each student, which is good.
With some
basic analysis, though, you can see how the kids move through the classes over time since the ids are the same every year.
There's five kids from the guy's class last year in his class this year. (Another class that has three of his friends has eight kids from his class last year.) There's seven kids in his class this year that were in his class two years ago.
Only one kid has been in the same class as the guy this year, last year, and the one before that.