Be a good role model and show that you're listening and interested in what he has to say. Don't fidget or shuffle papers. It's not necessary to maintain eye contact if it feels awkward, just pretend that time has frozen for a few seconds and will resume when he gets the word out. If someone else says something rude or demeaning about it, respond (to the guy with the stutter) with, "no, it's okay just take your time, your point about *insert topic being discussed here* is a good one." My boyfriend always feels like nothing he has to say is important enough to struggle through his stutter for. It's his job to keep trying and my (or your) job to make sure everyone else knows to listen and be patient.