Abstract: A reducer block for effecting the transition, in a block wall, between a course of first blocks which have a first front-to-back thickness, and a course of second blocks which have a second front-to-back thickness that is less than the first thickness, wherein the reducer block has a slanted rear face, whereby the reducer block has a thickness at its bottom surface substantially equal to the first thickness, and a thickness at its top surface substantially equal to the second thickness. A method of constructing a wall with the reducer block comprises the steps of (a) constructing a base portion comprising at least one course of the first blocks; (b) laying a plurality reducer blocks in a single course on top of the uppermost course of the first blocks, so that the bottom surfaces of the reducer blocks are joined to the first blocks; and (c) laying a course of the second blocks on top of the course of reducer blocks, so that the top surfaces of the reducer blocks are joined to the second blocks.