My 11 y/o lies all the time and is giving up in school

My 11 year old son lies to Mom and I all the time. The lie could be about anything too. Something simple as did you brush your teeth to homework not being done or having lunch detention for four days. He is a very bright kid! He avoids any self responsibility. He answers everything with I don't know, I forgot, or simply places blame where ever he can. Need help! I don't know how to stop this before it gets too carried away.