I had similar situations back in school and my tricks were to be occupied with something else prior the calling (but still half-listening) - for example small talk with friends (if possible), acting like I’m trying to find something in my bag, tying my shoes etc so that when I’m being called, because I’m “occupied” with something else, the calling isn’t my main focus (even though I’m basically tricking myself). I can’t explain exactly what psychologically happens but maybe I get the “comfortable” silent time before saying “here”, or that such situation allows me to say louder “here” because I’m allegedly surprised and when speaking loudly stutter rarely occurs. Another trick was to silently start with “eeerrrrrmmm” before expecting to be called. This kind of breaks the ice of starting to speak and doing so before teacher even says my name puts me 1 step ahead. This of course makes sense if the calling isn’t random and you know when you can expect your turn. Try different things and see what works for you. Best of luck!