Hello,
Information such as ADHD can be quite helpful for educators to assist with a child's education. If you request for this acknowledgement to remain private and confidential among the staff that need to know then it should remain so. Ask for this request in writing with the letter dated and signed. Make sure that copies are included in the child's folder, too. Also, please don't forget to include the school nurse, especially if she is on any medications or other medical treatments.
However, on another note, ADHD is a medical diagnosis with psycho-social implications and you should not feel that you need to hide this diagnosis. Many children with ADHD are the bright shining stars in their classrooms and go on to be very successful adults. As an educator, I always appreciated knowing if a child had any medical or developmental disorder so that I would be able to modify any lessons or progams to match their needs (e.g. such as more frequent breaks or shorter assignments) You may wish to learn more about ADHD and how to interface with the school personnel regarding this diagnosis at the website below.
Good luck!
Louise Masin Sattler, NCSP
Nationally Certified School Psychologist
Owner of Signing Families
http://www.SigningFamilies.com