Hello, my boyfriend and I have been together for a year and a half now and my son (whom is 5) thinks that he is his real father, which of course he is not. They have a real father-son bond and we are working on him to adopt my son, but for the mean-while can my son use my boyfriend's last name? He is going into kindergarten this August and I don't want him to find out that he is not his real father, because obviously his last name isn't the same as his, so he would end up finding out in school if we can't use my boyfriend's last name... and he also calls himself by that last name too... please help!

No, he cannot.

He needs to be legally adopted first. When you register him for kindergarten you will need his birth certificate and his shot record. The school, as a government agency (if he goes to public school) must use his legal name for recording purposes.