Irena my DS9 has a diagnosis of combined type ADHD and he's not medicated, and I notice a huge difference from year to year depending on the teacher and the classroom dynamic. Imho you are probably absolutely correct when you say your son did not suddenly get worse. It's likely the class/teacher change that is the culprit. Also keep in mind that some teachers are harder markers than others... that could be what's going on as well.