This answer deals exclusively with non-immigrant students; that is, students who are not residents of the United States and who are in this country temporarily. If a student who is not a citizen of the United States nevertheless lives in Iowa with his or her parents, the school district of residence is required to provide a tuition-free education to that student. This is true even if the parents of the student are in this country illegally. See Supreme Court's 1982 decision in Plyler v. Doe, 457 U.S. 202, 102 S.Ct. 2382. 72 L.Ed.2d 786 (1982).
No, there is no requirement that a district enroll a non-exchange foreign student living with a family in the district. The district is prohibited from enrolling non-exchange foreign students unless it is registered with the Student and Exchange Visitor Information System (SEVIS).