The Excalibur Kid(1999)

Zack doesn't have your ordinary adolescent problems. Transported back in time to medieval England, he lands in the middle of a vicious battle between an evil witch and Merlin, the master sorcerer, for control of Arthur's kingdom. It's up to Zack to help Merlin and Arthur reclaim the magic sword Excalibur and return Arthur to his rightful place on the throne.