Although the vast majority of business schools will not say that they require their applicants to have full-time work experience prior to application or matriculation, all business schools will say that full-time work experience is highly recommended or strongly encouraged.
On average, business schools like to see applicants with at least two years of full-time business experience—four to six years of experience (or more) looks even better.
What kind of work experience are business schools looking for? It varies. There isn’t a “perfect” type of business school work experience, although it should ideally be full-time, and you should have demonstrated managerial skills, a solid work ethic, and a history of added responsibility and advancement.
Why do business schools prefer to admit students with considerable work experience (as compared to medical schools and law schools, which don’t require any work experience)? For students applying to law school and med school, there isn’t really a place you can go to practice in the field without a degree (of course, you could make the argument that paralegals and nurses work in related fields, but they aren’t really the same job as the job you would get after the degree). Business, on the other hand, offers extensive options for working in the (nearly) exact field you will work in once you have your degree. That's why they require the experience. If law schools and med schools could do it, they probably would, but they can't. There are many reasons by business schools prefer work experience, but the primary ones are class discussion, classroom diversity, a greater ability to apply the concepts learned in class to personal experiences, and increased employment prospects post-graduation.
Classroom discussion
Students with prior work experience can draw from their own personal knowledge of the business world, and bring this knowledge with them into classroom discussion. This benefits the other students in class by broadening their knowledge of other work environments, workplace challenges, and managerial styles.
Classroom diversity
Students who have spent considerable time in the working work typically have a much broader range of experiential knowledge than students who have just graduated from college. This allows schools to admit a class filled with students who they know are coming from various backgrounds, which ensures than classroom discussion, student groups, and student body interaction will be rich with variety.
Ability to apply the concepts learned in class in a practical way
Students with prior work experience can immediately take the concepts they learned in class and apply them to their own professional past. This allows both for a faster comprehension of concepts and an easier time using the techniques and information in classroom discussion and practical ways.
Increased employment prospects post-graduation
Students who graduate from business school with an already-established track record of employment will have an easier time proving to potential employers that they have the skills and motivation necessary to succeed at their company and apply the knowledge they obtained from their MBA program.