What would cause a child to have such strange speech patterns?

My seven year old grandson, Jaden, is borderline autistic and he has some speech issues and some behavioral issues. He’s also been diagnosed with ADHD (though I don’t see it….) But he’s gotten much, much better since Chris, my son, came into his life about 2½ years ago. He is also a brainiac! One of the smartest kids I’ve ever known. Unfortunately, he often uses his smarts to manipulate people around him.

I think his biggest problem is with the “TH” sound. He puts his tongue on the back of his teeth instead of between them. He is in speech therapy at school. He’s also REALLY soft on the consonants which makes him very hard to understand sometimes. So he does have some valid speech problems, but he also exaggerates them at times and it’s really annoying! He’ll also revert to baby talk, especially when his little sisters are around, because he’s trying to get the same kind of attention they get. I finally got him to stop calling a “computer” a “puter.” He can say “Com” just fine, but, for what ever reason, wanted to hang on to the toddler version of it.

The other day he started pretending he couldn’t say “Vanta” the cat’s name. This was after he’d already said it a dozen times. I asked him if he could say “Santa,” and he could, so I said,“It’s just like ‘Santa,’ only it’s ‘Vanta.’ ” Well, he was eating his lunch and he kept saying things like, “Vanguh? Is it Vanguh, gramma? Is it ‘Vanger’ Gramma? Is ‘Vanger’ right, Gramma?” Well, I knew what he was doing so I just ignored him and he quit after several minutes. Now he calls the cat “Avanta,” but that’s understandable. He’s relating it to similar words he already knows, like, “Advantage,” or “Advice.”

But he also has some strange speech patterns, and I can’t figure out where they come from. For example, he may say “Why does he does that?” but he pronounces both of the “does” as “dues.” There is no such variation on the word ‘do’. It’s not anything anyone in his life, or in the English speaking world, would say, so where would that come from? Some of his stuff is plain old bad grammar, “He don’t do that,” and that kind of thing, but some of it is inexplicable to me.

Any ideas?