Interestingly, there have been studies that indicate that there is a sound relationship between a students' scores in Geometry on standardized tests and their success in college. But, this study is just one effort in many to come to a viable measure of high school students' potential as students of higher learning.
Nowadays, a high school transcript is a poor measure of a student's ability because grades are very inflated. Years ago, there was an article published in Reader's Digest entitled, "What has happened to the Gentleman's C?" This article examined the inflammatory character of grading systems in the Ivy League universities since the 1960s. It is clear that an number of factors go into grading that hitherto did not. In the 1950s, for instance, teachers rarely averaged in homework or class participation into a grade as is so often done now. Nepotism, too, plays a part in some students grades. Perhaps their parents are important figures in the community; perhaps a student is a great athlete needed on the championship team. So often, then, grades are not always a true measure of students' accomplishments.
Standardized tests leave much to be desired as well. Some very successful college students who are extremely methodical and thorough often not make the highest scores on the SAT or ACT exams that are timed. Likewise, highly analytical people who are successful in college have often scored lower than others on timed tests because they spend so much time analyzing the questions.
In order to best evaluate the potential of a student, the accumulation of transcripts, standardized test scores, a resume of organizations and awards, and objective letters from teachers may provide the key.
When colleges look at students there are usually three areas of evaluation. First, there is the high school transcript. Second, there are standard tests - SAT, ACT and SAT II. Third, there are teacher's evaluations and extracurricular activities.
None of these are perfect measures of a person's potential. This is why colleges uses three standards to examine a person. With this stated, I would say that the best indicator is a high school transcript. The reason behind this is because it is a record of four years. The sheer length of measurement makes it the best indicator. For example, a person might have a bad day when it comes to a test. In light of this, the best indicator is the school record.
With this stated, we need to be aware that some students are late bloomers. We need to be open to this. For this reason, it might be a good idea to weigh the second half of a student's record more than the first half.