Jordan & David Co-founders, Admission Science
No, colleges do not have a set quota for the number of students from any particular high school. In other words, they are not pitting schoolmates against each other. Applications are read and evaluated independently of one another.
But, there are some caveats to this answer.
Many colleges have admissions officers who are familiar with specific states and regions. This gives them context to assess an applicant relative to other candidates from their region.
For example, Yale has an admissions officer responsible for applications from New York. That officer understands all the opportunities available in the state. They know which awards are more difficult to earn, and which are "fluff."
So while you aren't competing directly with your schoolmates, you are competing with other students from your state & region.
This is where quotas sometimes come into play. Some schools do have quotas on things like:
Percent of students from a state
Percent of students from a geographic region
Percent of students from low income neighborhoods or traditionally underrepresented backgrounds
These figures tend to change from one year to the next. For example, UCLA, UC Berkeley, and UC San Diego are reducing the number of out-of-state students they accept. The plan is to reduce out-of-state students from 19% to 10% of the freshman class over the next 10 years.
Okay, so what does this mean for you?
Get real data. Ask your counselor for data on how many students per year from your school get into your dream college. Through tools like SCOIR / Naviance, you can also get the GPA and test scores of the accepted students. This type of data isn't predictive of the future. But it does give you a sense of how competitive students in your school are vs. other students in the region / state.
Focus on what’s in front of you. Don't stress about beating that person in your class in GPA, activities, or whatever else. Focus on improving your own application and being the best version of yourself. That will help stand out more than just “doing what that other student did, but better.”
Take advantage of resources in your school and community. Many admissions readers will know your school and the options in your region. If there are well known or highly selective opportunities in your state, seize them.