1. The majority of learning happens in the first 3 years. The fourth year of medical school is devoted for electives and interview season. Once interview season is completed, there's plenty of downtime. Accordingly, the fourth year should be eliminated completely. Or it can be offered as an option for those who don't know what specialty they have decided upon. Students don't need to be in school for interviews and could spend extra time recuperating for internship or working part-time to pay off loans.
2. There is a shortage of doctors. We can increase the number of graduating MDs each year and accordingly address the MD shortage that affects our society. "The Association of American Medical Colleges predicts bigger shortages in all types of physicians: 63,000 by 2015 and 130,600 by 2025." This means more doctors to help meet the needs of underserved areas, entering primary care, and more MDs doing research.
3. Doctors already have too much debt. In 2012, the average graduating MD starts out with $170,000 of student loans. If medical school were reduced by one year, it could reduce educational debt by up to $50K. Additionally, there is the opportunity cost to consider of this extra year.
So how can we make it three years? All schools should offer the option of an accelerated curriculum for interested students. Medical students will be graded upon clinical competency and test scores. If they are incompetent or failing, then they simply don't graduate.
