Whether there is a difference in the performance of public school and private school students on the advanced placement (AP) tests of the College Board was studied. The sample was composed of 216 public high schools, 32 Catholic high schools, and 24 other private high schools in Northern California, all of which gave their students at least five AP examinations. Subsamples were used to compare schools in the same locality. In the sample as a whole, private school students slightly (but not significantly) outperformed public school students. In a subsample of 148 schools, comprised of 44 schools with highly developed preparation programs and 104 schools which might compete for students with these schools, Catholic school students were outperformed by public school students, and public school students were outperformed by other private school students. Catholic schools were less likely than other private schools to have highly developed programs of preparation for the tests. This study demonstrates that the sector the school occupies has no significant influence on this aspect of student performance and illustrates the importance of the quality of the school's program on performance on AP tests. Four tables give information on students test results. (SLD)