An education degree is in some ways like joining the army, navy or air force, or working for a company who is happy to pay college tuition fees for courses which are beneficial to you doing your job. In the armed services, joining an ROTC program will pay for your education in exchange for promised services to the armed forces in the future. In some states, a degree in education can work much the same way.
In America, there is currently a shortage of teachers in many areas of the country and many subject areas. Of course, there are subject areas where there are virtually never shortages, such as high school English teachers or early elementary school teachers; somehow, the appeal of teaching these two things seems to be very large, making it unlikely to have a teacher shortage. Other subjects, on the other hand, often experience shortages, especially in extremely rural and inner city locations. Fields of education that often experience teacher shortages are in the sciences, math, and in foreign languages.
This lack of teacher personnel makes it so that schools are in need of more teachers who are qualified with the right college degree to teach the subject in question. The No Child Left Behind Act has made it even harder for schools to hire professionals who clearly know their subject well, but who don't hold a degree in education. For example, a chemical engineer often makes a terrific chemistry teacher, but the No Child Left Behind Act makes a degree in chemical engineering unsuitable for teacher qualifications. In most cases, the individual with a degree in chemical engineering can be employed as a teacher under a provisional certification, on condition of completing required education classes to earn teacher certification. In many of these cases, the school district will pay for the courses the individual has to take; if the professional is filling a teacher shortage area, it is highly likely that the college courses in education will be paid for.
The above example shows how a degree in education can be earned without paying for it, by letting the school district for which one works pay for the university courses needed to gain teacher certification. While this is attractive, students right out of high school do not have this option because they can not teach without a college degree. However, there are other ways to earn an education degree (as a bachelor's degree) without paying for the degree oneself. These options are quite similar to Army, Navy and Air Force ROTC programs.
In such programs, students sign a promissory note that declares that they will be teaching in a given state once they receive their bachelor's degree. Upon successful completion of their degree, they must start teaching in the state they promised to teach in. If they do so, all of the money that they received for signing the promissory note is forgiven at a pre-arranged rate; if the graduate does not begin teaching in that state, the money received has to be paid back in a similar fashion to other educational loans. Students who go on to graduate school can defer their teaching to after their second graduation, although interest does start to accrue. Should you decide NOT to teach in the future, all the money that you received as an undergraduate has to be repaid, plus the interest that has accrued.
Different states have different programs. I attended my alma mater on such an agreement with the 'Teachers for Maine' program by the Finance Authority of Maine (www.famemaine.com); different states will have different programs, depending on teacher shortage areas and projected shortage areas for the future.