Even working with word problems. Give him “silent processing time”. You can set a timer where he’s not “allowed” to talk. It (paradoxically) creates space for him to gather his thoughts and maybe not be anxious. I stutter no matter what. It means nothing about how I feel- it’s seriously just how I talk. It gets worse and better randomly. So you’ll have to get to know him to figure out his personal patterns. We’re all different.