Michael (Unknown surname) is a student in Astrid's AP math class. He is fifteen so poofs out when the others disappear.
Michael's mention in the series
Astrid describes him as 'better than me' at mathematics, which must mean he is a very good student, but they were in the same class as Michael had dyslexia which held him back. Prior to the FAYZ they were having a lecture on polynomials. There was also another student in the class who Astrid calls 'Jink'.
Significance of Michael === It is the disappearance of Michael and Jink, along with the adults, that first leads Astrid to make the connection between the disappearance and the age of fifteen. Michael is not mentioned for the rest of the series but it is presumed that he continues life as normal on the outside.