What should I do? A kid in my class continues to make racist remarks?

Okay, I will make my best attempt to abridge this explanation, but no promises... So, I am 15, and I am currently a freshman in high school. I have been close friends with my friend, Johnny, for about 7 years now. Johnny's parents moved abroad from South Korea to America early into their marriage, and had three children after they arrived, including Johnny. Anyways, I have math class with Johnny, and we were lucky enough to be seated right next to each other. And in this math class, there is a kid named Sam; Sam constantly says racial jokes to Johnny, and simply doesn't stop. I'm not sure if you will be able to understand the example I am about to give you, but I will say it anyways... So, every time Sam sees Johnny, he glances at Johnny, and goes, "Deh neh neh neh neh neh nuhh nuhh nehh." I know you don't understand, but this jingle is in the song, "Everybody was Kung Fu Fighting". Not only does he do this, but he will also call Johnny "Ching-chang-chong", and all of this other racial bullshit. Johnny isn't the type of person who is going to argue, so he stays quiet, and will complain a little to me. "God, he is so annoying..." The only thing Sam's actions do to Johnny is make him depressed. After continuously asking him to please stop, and Sam saying, "Aw, c'mon mayuhn... It's Johnny, I ain't bein' racist...", I finally told my math teacher what was happening, and asked her if she could please move Sam away from Johnny. She did, but about a week later, she made many changes to the class's seating, and Sam is right next to Johnny and I once again... And, it isn't just around Johnny, Sam is also a racial bastard when Johnny isn't around. So, right after math class, I have Graphic Design. In this class is Sam, and my friend, John, who is a junior. I met John in this class back in the beginning of January, and we get a long great. We have a lot in common, and as it turns out, he has ADD like I do... So, after our conversation about ADD, we were already good friends hahaha... But, one day, Sam and John were on the subject of homecoming, and Sam asked John if he had ever been before. John said yes, and Sam asked who he went with. John said, "my girlfriend at the time", and pulled up a picture on his phone of himself and the girl both at homecoming. John showed both Sam and I, and as I looked at the phone, I saw the girl, who was very cute and attractive. And as it turns out, she was Asian. Then, out of nowhere, Sam asks John, "What's her name? Bing-Bang-Ching-Chang-Chong?" John didn't say much, but became very pissed off at him. I kept telling Sam that what he was doing was racist, but he always denies it. From what I can tell, he mostly discriminates the Asian race. So, as a result of him being a racist piece of ****, and refusing to stop after I ask him nicely, I have decided to talk to the counselor at school tomorrow... I face one dilemma: Even if my name remains confidential, and Sam gets called up to the office, he will know it's me that reported him... I am going to go anyways, because I realize that bullying is a larger situation than Sam knowing I reported him... But, do you guys have any tips? These are just a couple of examples from the many more racist things he does... By the way, Sam is Caucasian, I am Caucasian, and John (not Johnny) is Caucasian as well... Thanks a lot, and apologies for such a long story... -Russell