L.O.
I think the current recommendations are NOT to hold kids back. That kids that are held back feel bad about themself.. bad about school.. and sort of give up.. In the long terms.. kids that are held back are more likely to drop out of school.
Talk to your dr and see if he will give you a prescription for behavior modificatin therapy. A friends daughter with ADD ..(also in kinder also young for grade.. also very very distractable...) is in behavior modificatoin and they are hopeful. Do not be afraid to try medicine .. it is a TRY.. if you try if for a week or a month and your son was much better behaved and much better mood.. then the medicine is a good thing.. if you try it and it makes him drugged and sleepy then it is a bad thing and you dont have to do it anymore.. peopole are so afraid to try mediciine .. but for some kids it is so so helpful.