Purpose: The purpose of this study was to examine differences between boys and girls in their performance on STEM related AP exams. Specifically, gender differences were examined for the following STEM related AP exams: Calculus AB, Calculus BC, Physics B, Physics C: Electricity and Magnetism, Physics C: Mechanics, Chemistry, and Computer Science A. Archival data from the College Board were utilized to compare the performance of boys and girls on the STEM related AP tests administered for 1997 through 2012 school years. Methodology: A nonexperimental, causal-comparative research design was used to compare the performance of boys and girls on STEM related AP exams. Pearson chi-square tests were conducted to determine the extent of statistically significant differences in STEM related AP exam score distributions for boys and girls. Additionally, cost effectiveness ratios were calculated to measure the effectiveness of the monies spent on exam fees by students attempting AP exams. Findings: Statistically significant differences were present for each of the 16 years for all 10 STEM related AP exams. For each STEM related AP exam, a higher percentage of boys than girls earned passing scores. Participation in the AP program increased for both boys and girls across this 16-year time period. The percentage of students earning a passing score increased on the following exams: Calculus BC, Physics C: Electricity and Magnetism, Physics C: Mechanics, and Computer Science. During the same time period, the percentage of students earning a passing score decreased on the Chemistry, Biology, and Environmental Science exams. Little change in the percentage of passing scores was noted for the Calculus AB and Physics B exams. Cost effectiveness ratios were calculated to measure the effectiveness of monies being spent on AP exam fees. For boys, cost effectiveness ratios were negative only for one year; however, girls had negative ratios for six of the 10 AP exams analyzed. Thus, monies paid for AP exam fees were spent more effectively for boys than for girls and millions of dollars were spent by students failing to earn passing scores on AP exams. Implications of these findings for school leaders are provided. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]