He is in first grade and is 7 years old. His teacher has never mentioned the possibility of ADD, but I wonder if he has this condition because of the recent improvement on medicine. Imipramine is a medicine that can commonly help this condition. The medicine is helping because he is getting a better quality of sleep at night, improving his daytime ability to concentrate. The imipramine is treating an underlying anxiety disorder.
Some children have school phobias which manifest as poor school performance.
Chronic poor performance can cause low self-esteem which is commonly a symptom of depression. Imipramine is an antidepressant drug that can treat a variety of conditions. If there are other relatives with the diagnosis of ADHD or other learning disorders, I would vigorously pursue this possibility with his teacher and his doctor. If there is no family history of such difficulties, you might consider watchful waiting. By looking at the characteristics of ADHD, it seems my son who is going to be 4 on November 19th could possibly have this disorder.