If the school has completed questionnaires on your son, ask to fill one out too! If they don't allow you to, I would be suspicious. Most schools want parent input before making a decision regarding a child and offering them in school services.
On this point specifically: the most common rating scale for ADHD used by pediatricians is the Vanderbilt. pdfs are freely downloadable for this. Here's one:
http://www.uwmedicine.org/neighborhood-clinics/Documents/03VanAssesScaleParent%20Infor.pdfAnd here's the teacher one, if you want to get input from a different observer, like an afterschooling tutor, coach, or extracurricular instructor:
http://www.nspeds.com/_files/Vanderbilt-Teacher-Initial.pdf
