M.P.
My grandson is now 4 and still sucks his tongue which he holds poked out of his mouth. He's been in speech therapy for a year. There are a couple of conditions for which tongue sucking and poor speech are indicators. You can have him evaluated by the school district and if he's in need of services to enable him to be a success in school they will provide those services without cost.
Now, my mother and my youngest brother, who is now 50, have chewed on their tongue since I can remember. Their speech has been OK. They say it's comforting.
I don't know if this helps but it's 2 different views on tongue sucking.