Advanced Placement courses and their grades listed on a student's transcript. Note that although grades are important, high grades with no AP courses will make a student less competitive. Not all schools provide this information. Make an effort to have the high school submit it if at all possible. High schools vary in quality which often leads to grade inflation.
Class rank tends to reveal the students who stand out as competitive in most of the academic areas.
ACT or SAT scores. Students have several opportunities to take these tests for practice before their senior year in high school. The exams are not free, but the benefits of experience, reduced test anxiety, and higher exam scores make the costs seem trivial. Most agree that TAG students should take these exams more than once. Check with a school guidance counselor about the options.