A: I cant speak for Lubavitch since I am not a chabadnik and am not familiar with their speciifc minhagim Actually, a Barmitzva does not have to do anything, once he turns 13, he is barmitzva. My father in Europe was called to the Torah on a Monday, and his mother made some cake and schanpps and that was it. But our custom is to do it on a shabbat, train the boy to know the torah blessing, the haftara, and with those who have a good education, leanr to read from the torah and the lead the davening. This shows a mastery of shul skills. Saying a nice dvar torah also shows that the boy inquestion undersdtands what he has come to in life and has a decent Jewish education.