Most admission officers agree that the most important part of your child's application is their high school transcript. Colleges want to see that your child’s taken certain courses to help them decide if your child is prepared for college. They also like to see that your child has taken challenging courses like AP, IB, or honors courses. And, of course, they want to see that your child has maintained a good grade point average.
What's the second most important factor? There's no one answer to that question. Some colleges look at SAT and ACT scores next, but other colleges place more importance on the essay, letters of recommendation and/or extracurriculars.