Calming the 6th grade beast

Since the first day of school the behavior of one particular student has been atrocious. I had to give this student a school citation the very first day of school, before I had even talked to my students about the classroom expectations! I had never seen anything like this before. This persons behavior was an obvious cry for ATTENTION! He/She was fidgety, roamed the classroom, talked out at any time of the day, and drove other students crazy with constant babel and noise making, and this was the first day of school! I called mom and got the response I was least expecting. Her child says it is other kids with the issues and that whatever her child tells her, she is going to believe. So we were off to a "lovely" relationship. NOT! Since that day, I have tried everything I could think off, my principal could think of, and the school councilor could think of. Let me just tell you what we have tried. Simply following the natural course of the classroom consequences. We tried tally marks every fifteen minutes. We tried to create a contract with mom, but you can imagine where that went. I have tried putting his/her desk right next to mine-all that did was give him/her full access to me. Huge mistake. We have done think time, we have done detention during recess, I have classroom parties with the invitation being "no bad behavior"-nope. And just today, I had to go through the entire spectrum of consequences. I have gotten no where. Help!!