There are some hospitals in the past who have required osteopathic students to pay a fee (out of their own pocket) to rotate there. Your school probably pays some hospitals, like the ones they have affiliations with maybe, but not others. Some schools don't pay any of the hospitals. Most of the teaching hospitals don't really need a fee. They like to have students rotate through because these students may eventually become residents. The hospitals are paid by the government (over $100,000/yr) to train residents and it is a part of their income. They want you there. Non-teaching hospitals don't really care all that much whether or not they have those students. In some case students can just be a burden-- unless they stand to gain monetarily from it. Hence, the payments from your school or out of your pocket.