Hi Gill,
I've worked successfully with slowing down speech (and internal images) with children. I'm working now with a 10 yr old boy recently referred for anger problems - who also when excited 'trips up over his words' .. and has a slight stutter/hiccups. He's readily taken to eft , and is very creative; so I'm hopeful of progress .. 'will let you know of any developments/ideas we come up with! Now we're up and running, I'm going to try tapping from the perspective of the word itself ..
Eg - "Even though I'm just a simple word and just want to be heard this tight throat gets in the way, but I know I'm wanted by [name of boy] and so will slip out anyway!"
Just fishing for now to notice where there's resonance .. expecting lots of laughs .. and hiccups to start with!
Good luck with your son - does he speak fast? Does he process 'visually busily' would you say? (Do his eyes look/dart around excessively when he's busy thinking?) If so, it may be that you can use eft to slow the internal images down (his cinema inside), which would then in turn ease the speech. Just an idea!