If it were me, I would not sign the permission. You already have a professional assessment that says he is not ADHD. I had to fight hard to keep the school form labeling my son and wanting to drug him so they didn't have to deal with the fact that he was bored, under challenged and gifted in an inappropriate setting,

Also gifted testing is not a reward for good behavior - it is testing to place your child in an appropriate setting because the one now isn't working. Special Ed is for kids who are not served appropriately in a regular classroom setting with no accommodations. Gifted is special ed. I'd push for the testing. You'll find it alleviates a lot of the acting out, joke telling, etc. My older son was misbehaving before I got him tested. After they moved him to gifted, he was much better behaved. Not perfect by a long shot, but much better.