My advice: Above all, stay calm and neutral (as I’m sure you have done). On the first offense, issue a warning (call it a “check” or something like that) to the child in a kind and empathetic way. Same with the second time. On the third warning, he loses 20 minutes of TV or play time. Stay neutral and calm during any meltdowns. I know this is difficult, but as someone with ADD who parents a child with ADD, my opinion is that the three-tiered approach would help him the most. You’re not increasing the shame or anguish this way (not that you would; you sound very kind), but letting him know there are consequences if the behavior continues. Sometimes it takes some of us with this problem a little while to learn to adapt without blurting out things, so losing privileges after one time of blurting something out can be defeating and cause further issues and problems. If we’re on a warning system, we have time to think about it before it happens the next time.