Why does Year Twelve retention differ between Australian states and territories?

Year Twelve retention rates have a number of well-known deficiencies that prevent proper comparisons of school completion between school systems. This paper compares secondary school completion rates across Australian states and territories from 1989 to 2002 and adjusts 'official' 2002 retention rates to take account of the acknowledged measurement problems. We identify a pattern of mismeasurement of national Year Twelve retention over the 1990s. We estimate that the Year Twelve retention rate was a particularly poor measure of national school completion in the early 1990s, when it appeared to peak in the official estimates. In contrast to the official figures, our adjusted measure of Year Twelve retention was no lower in the late 1990s than it had been in the early 1990s. Our findings suggest that governments should be cautious in using official Year Twelve retention rates as a measure of the performance of Australian school systems.