Hi, what really seemed to help with my DS's stammering was the following advice: to get down to his level, place a hand on him gently and wait patiently (not to try to "speed things up by verbal assistance"). This did take a few weeks, but worked very well. In our case the situation wasn't helped by an older DS always speaking over him (difficult for the younger one to get a word in) so we had to deal with that too. I'm not sure if that is because the stammering had been a fairly recent thing anyway so was easier to sort out. I agree with trying out various groups (if you aren't already) as this may help. Sorry I don't have anything more..
