Post-anthesis water deficit and increasing vapour pressure deficit are common and can result in reduced grain yield and the development of small or shrivelled wheat kernels (screenings) that reduce grain value. Previous studies suggest incorporation of a tiller inhibition (tin) gene to restrict tiller number and thereby slow water use and promote the development of larger, fertile spikes to increase kernel weight. This paper reports on the influence of the tin gene on grain yield and screenings in multiple wheat genetic backgrounds assessed in field experiments in 2005 and 2006. Across environments, grain yield ranged from 0.90 to 5.50 t/ha and screenings from 4 to 20%. The effect of tin on grain yield and screenings varied with environment and genetic background. Grain yield was unchanged in tin lines derived from varieties Brookton, Chara, and Wyalkatchem assessed in southern Australian environments. However, there was a 31 and 10% advantage of free-tillering over tin-containing Silverstar lines for the 2005 western and 2006 northern experiments, respectively, resulting in an average 12% reduction in grain yield of Silverstar tin lines. In northern experiments, where screenings ranged from 4 to 12%, Silverstar-based tin lines produced significantly fewer screenings than free-tillering sister lines. Reduction in screenings was associated with a higher kernel weight ( 10%) and a tendency for lower grain yield, although individual Silverstar tin progeny with grain yield equivalent to the parent were readily identified. The incorporation of the tin gene has considerable potential to reduce the incidence of screenings in commercial wheat crops. Variation in grain yield associated with the tin gene was dependent on genetic background, with potential for selection of higher yielding tin progeny for commercial line development.