Any Ideas?

I have a friend whose son is 4 years old. He doesn't talk much at all, he goes to school full time in prek, he will do some gestures but overall seems a bit off.
Hes in speach/language classes ect. He has a bit of a short attention span. He has not been diagnoised with anything yet, specialist hasn't called back. Most I know of is the doctor said he seems to have an issue with putting out that he understands or knows something. Like he knows the word but it doesnt come out or takes longer to. Hes made some improvement where he said a sentance regarding a toy that fell instead of gesturing or making sounds. But its random times when he will to such, not a constant.

I am wondering if any one has any ideas of ways to help him open up and work on communicating.