A method and assembly for producing substantially tar free product gas from gasification of carbonaceous material. The assembly preferably includes a first stage gasifier to produce char-ash and tar laden product gas and a second stage gasifier which has a char-ash heating zone, at least one cyclone, and at least one standpipe for the purpose of allowing selective delivery of char-ash to the char-ash heating zone. A char-ash heating zone that utilizes oxidation of char-ash is preferred and this results in the heat required to convert tar, additional yield of product gas, and an oxidized, activated carbon surface to facilitate tar conversion in the riser, thereby reducing the temperature required to achieve the desired tar conversion. Alternatively, external heat is supplied to the heating zone.