Tiering is a multi-stage test design whereby teachers allocate students to a particular difficulty level (tier) of a test. This approach to the challenge of delivering assessments to students with a heterogeneous ability distribution is normal practice in UK public examinations at the age of 16. This study uses Item Response Theory number-correct score equating to examine the relative standards that are set between tiers on certain GCSE assessments. It finds evidence to suggest that candidates on the foundation tier are being over-rewarded, while those on the higher tier are being under-rewarded. It concludes that the use of IRT test equating could help improve standard setting on tiered tests and that the issue of restricted grade ranges on these tests may need to be reconsidered. (Contains 2 tables and 2 figures.)