I stuttered as a young child. It's not unusual for developing children to stutter and many children outgrow it. I've learned that those who continue to stutter after young childhood may stutter their entire lives as I did. You inferred your son’s fluency improved earlier with therapy, but recently recurred. It seems he was aware of his stuttering when he was younger, but he's not aware now? I stuttered all my life until I was 70 when I became fully fluent. School was difficult. Being marginalized was horrible. I wish my parents would have started speech therapy before I was in elementary school. As you have said your son is unaware he stutters, it would be cruel to expose him to embarrassment from other children. As a former stuttering child, I’d rather be prepared by my family than be taunted by other children. Continuing with the right speech therapist, as soon as possible, can teach your son techniques to make speaking easier. My parents never shamed me, but never took any steps to help me. I was fully aware I stuttered and dreaded reading aloud, doing presentations, and asking or answering questions. Had I had the opportunity to learn techniques from a speech therapist, my youth would have been so much better.