Abstract: An interlocking concrete block for forming horizontal wall-channels for reinforcement of block walls of dry-stack, vertically-offset, double-wythe construction. The block has an outer block wall on one side and a head portion extending to the opposed side. The head portion has a connecting portion which interfits with a receptacle of a similar block. The block has a channel extending generally parallel to the outer block wall. In a block wall, two vertically-adjacent series of the blocks form a horizontal wall channel which can hold a reinforcing bar and in-filled concrete, for horizontal reinforcement of the wall.