This article describes the construction of a common scale which attempts to span the English language ability range of students in the Hong Kong secondary-school system. The purpose of the scale is principally to give English language teachers a reference point - a 'snapshot' - of their students' ability level so that they may access materials in a testing database at points of ability which are appropriate to different groups of students. The testing database - the TeleNex test bank - has the objective of providing English language teachers in Hong Kong secondary schools with professional help and support with their school-based testing. The article describes how tests with common items were designed for a range of secondary-school forms in Hong Kong and how the common ability scale was derived from the resulting bank of items. The article suggests that, while the sale has been established as a reference point for the test bank, it may well have more general use within the Hong Kong educational system. Copyright © 1995 Edward Arnold.