Test performance of high school students on the Armed Services Vocational Aptitude Battery (ASVAB), the General Aptitude Test Battery (GATB), and the Differential Aptitude Tests (DAT) was compared. The design of the study provided for information on test intercorrelations, prediction equations for the ASVAB tests from the commercial tests and conversion tables between highly similar tests across batteries. Separate comparisons were made by grade and sex. A total of 1,232 students were tested and each student took the ASVAB and one other battery. Six of the tests in the ASVAB correlated highly with tests in the commercial batteries. The remainder of tests in the ASVAB were information type tests that had low to moderate correlations with the tests in the commercial batteries. The correlations for the males were generally higher than for the females and the correlations increased with grade. The multiple correlation coefficient in the prediction of the ASVAB tests from the commercial tests ranged from zero to .90. (Author/MV)