There are multiple parts of a completed admissions application, and each college requires something slightly different.  Included below is a comprehensive list of what could be required in an application, along with who will often be required to make the submission.

Submitted by you

1) The Application – Some colleges have their own unique application form.  Others use the Common Application, which can save you substantial time by allowing you to apply to multiple schools through a single portal. Regardless of the format, colleges often ask for the following on the application form:
  • Personal Information– Input your name, email address, phone number, high school, college credits already earned, standardized test scores, citizenship information, etc.
  • Extracurriculars– Explain what you’ve done outside of class, and how much time you devoted to it.   In addition to traditional extracurricular activities, remember to include part-time jobs or other obligations like taking care of siblings.
  • Summer Activities- Explain summer jobs, internships, or other enrichment opportunities.
  • Essays – Submit the essays that you’ve written.
  • Honors– List any honors you've received along with the context.  How many students competed for the honor? How many students received it?  Why is it important?
  • Disciplinary Infractions– Detail information on any suspensions or expulsions.
  • Application fee – Pay for your application to officially submit it.  If the cost is too high, speak with your guidance counselor or the college's financial aid office; fee waivers are often available so that you can submit the applications for free.
2) Standardized Test Scores – In addition to listing your SAT and/or ACT scores on your college application, you will be required to submit official score reports.  These must come sent directly from the College Board (SAT) or the ACT to the college.  You can select colleges to receive your scores while you are registering to take the tests, or you can do it later when you get your scores back.  Many colleges also ask that you submit results for AP or SAT Subject tests that you've taken.

Submitted by your guidance counselor

3) Official High School Transcript – The official transcript lists each of the classes you have taken during your time in high school, along with the grades and credits that you have earned.   The transcript is usually sent directly from your high school to colleges by your guidance counselor, so be sure to inform him/her of each of the colleges where you are applying along with the relevant deadlines.
4) Mid-Year and Final-Year Grade Reports – The initial transcript that you submit with your college application only includes grades through your junior year.  Colleges want to make sure that your trajectory in high school continues and that you finish strong, so they typically ask for an update on your grades from your guidance counselor after the first half of your senior year and again once you finish senior year.  Colleges do reserve the right to change their mind about your admission (specifically, reject you after you were already accepted) if your academic performance takes a nosedive.  This doesn't mean that if you get one B in your senior year that you are in trouble, but it does mean that all Cs and Ds in the final semester from a student who otherwise earned As and Bs might be cause for concern.
5) Secondary School Report and/or Counselor Recommendation – The secondary school report allows your guidance counselor to place your academic experience in context.  They will typically provide information on the number of advanced placement courses offered at your school, your academic strength in relation to your class, the number of students at your school who attend college, etc.  The counselor will also have a chance to provide information about other special circumstances you may have faced in high school and how you add to the academic and social community.  Colleges are trying to understand the big picture based on this portion of the application, and they are particularly interested in knowing whether you made the very best of your circumstances.

Submitted by your teachers

6) Teacher Recommendation – The teacher recommendation is meant to give colleges insight into how you perform academically within the classroom.

One Final Note

Even though several elements of the your application are submitted by others, you are still the person who is ultimately responsible for making sure that all parts of the application arrive on-time.  Be sure to check in with both your guidance counselor and recommending teachers – the earlier the better – to ensure they are prepared to submit their portions of your college application package.  You can then check the online portal for each of the colleges where you are applying to make sure that they have received all materials in a timely manner.

Source: Expert interviews and National Association for College Admissions Counseling resources