I'm an SLP in the schools.
when you say speech disfluency and his words are not clear, can you give an example? the reason I ask is that it sounds to me more like you are talking about an articulation disorder (speech sounds not being clear/correct).
also, if he stuttered between 4-5 and it resolved without speech therapy, it was probably just normal disfluency. a lot of kids go through this at at that age. of course, I can't say that for certain, but just wanted you to know that its highly possible this was a normal developmental stage for your DS.
are you getting the screening through the school system?
if its through the schools, my recommendation would be to be sure you talk to his teacher and make sure she is seeing the same thing and get on the same page. if this is something that only seems to happen in conversation, you need to make that clear to the SLP as well. I say this because there are times when a kiddo is absolutely unintelligible in conversation or the classroom setting, but can do the single words on my eval just peachy. Of course, the SLP *should* be observing other settings, and looking at connected speech. but sometimes they might miss this if the child is mostly quiet in their session or (as many kids do) speaks extra clearly because they know they are at the "speech lady."

I agree with what the PPs said. Your son has probably noticed. If he hasn't, he will in the future. So many people worry about the stigma of speech therapy but the truth is that kids love to come. Most of the kids in the class that I don't take out for speech are jealous and ask when they get to come to speech

Its really not something people are embarrassed of (unless perhaps they are in middle school and above, but even THEN most of my kids love to come to speech. surprised me, but its true).
I'd just be nonchalant about it and say that sometimes when he talks fast, it can be hard for others to understand and this speech teacher might have some "tricks" for us. Kids seem to like the idea they are going to learn "tricks."
HTH.
XOXO
B