The MCAT
Since things get hectic late in the admissions season, you'll have a distinct advantage over someone taking the August Medical College Admissions Test (MCAT) if you take the April test and get your applications in by late June. Even if you turn in your American Medical College Application Service (AMCAS) application early, the vast majority of medical schools will not look closely at your application until they have a copy of your MCAT scores.

According to the "AMCAS Survival Guide" you should "if possible, take the MCAT on the April test date." As evidence, they cite the admissions cycle--earlier is better. Of course, due to their academic schedule, not everyone can realistically take the April test. If you have not finished most of the prerequisites for the test -- two semesters each of biology, physics, general chemistry, and organic chemistry -- you should probably not sit for the exam.

Each year, many students are accepted with August MCAT scores and applications that arrived late in the process. Unfortunately, there are also a lot of students who are not accepted but would have had a decent chance had they applied earlier. Turning in your application early can certainly help to give you the competitive edge.