Construction blocks include transversely disposed first and second end walls, longitudinally disposed first and second sidewalls, and longitudinally disposed top and bottom walls. A recess is formed in a first end wall, a protuberance is formed in a second end wall and the recess receives the protuberance when the blocks are laid end-to-end. A longitudinally-extending protuberance is formed in the top wall, and a longitudinally-extending recess is formed in the bottom wall and receives the top wall protuberance when the blocks are vertically stacked. A pair of parallel, longitudinally-extending ledges is formed in the top wall of each block by the top wall protuberance and each ledge receives an associated bottom edge of a sidewall when the blocks are vertically stacked.