Since 1977 when the Australian Scholastic Aptitude Test was first used in the ACT as a moderating device, there have been differences in the average performance of males and females on the test. This difference in mean group performance has been referred to as a sex bias. This report investigated the nature and the origins of those observed sex differences in ASAT mean scores. Retention rates were investigated to determine the effects of different retention patterns for male and female students on their ASAT scores. Students' attitudes were explored to examine the relationships between sex, attitudes and performance on ASAT. Students' preparation was investigated. The problem of bias in the ASAT items was investigated using both classical and latent trait theory and the effects of course type on ASAT performance was investigated.