I personally always hated these situations and have struggled with them in the past. I've noticed that as they read names, the anticipation of my name being called made me very anxious. As a result my body tenses, especially in my stomach and jaw. I found that trying to remain loose and relaxed helps out a lot. If I feel myself getting tense I'll breathe slowly from my diaphragm and relax my jaw. Mindset also helps a lot. When I anticipate stuttering or put pressure on myself to blurt something out really fast I found that my chances of stuttering go up a ton. Not really caring and having the mindset of "I'm gonna do the best that I can and if I stutter then oh well" has really helped. That being said, it's ok to take a second or two or even three before answering. People who answer immediately only do so because they know their name is coming up next. There's no rule that says you need to answer .5 milliseconds after your name is called. You've probably noticed that the ones who are not paying attention have up to 5 seconds to answer and they'll even have their name called again just to confirm if they're absent. Use the 5 seconds you have to take a breath, relax and to say the word on your own time. No rush. At the end of the day nobody really cares about how fast you answer an attendance call, and nobody really cares if you stutter while responding. We are our own worst critic :)