If it helps, everything I've read on the subject indicates that "yes, a triangle, well done" is exactly right.

Everybody sometimes feels they don't have a clue.

How old is your son? My younger child was totally incomprehensible until past 3 - even to his parents - though the speech assessor agreed with me that his grammar and vocabulary were fantastic. He now - nearly 6 - speaks beautifully, with just a little trouble distinguishing s/sh, t/ch and r/w. He had a few sessions with the therapist when he was 4, though I'm not sure whether he'd have improved anyway.