Embodiments of the invention comprise an adjustable fence assembly for use with a power tool, that further comprise an elongated lower fence for attachment to the power tool, the lower fence having a base with an upper support and locking surface configuration extending along a substantial portion of the length of the base and a vertical front face for positioning a work piece, an elongated upper fence having a bottom surface configuration for engaging the surface configuration of the lower fence, the upper fence being releasably attached to the lower fence and adjustable relative to the lower fence along its lengthwise direction, and a locking mechanism carried by the lower fence and operatively connected to the upper fence for selectively applying at least a downward force and a face biasing force for securing the upper fence to the lower fence.