Located on the coast of The Island, The Monastery is home to a group of men and women who are primarily dedicated to the education of the children of noble families. Money from these families is strongly implied to be the primary source of income for the monks. Occasionally, the monastery will take in and raise orphans with the expectation that they will work within the monastery.
Caldan is the only orphan mentioned in ACoS which possibly indicated that he was a special case (the monks mention that his parents were frequent visitors) and that caring for orphans is not a common occurrence. This would also explain Caldan being dismissed from the monastery because of the controversy created by his presence (as a commoner) in classes paid for by the families of nobles.