That overhead you're speaking of is present with bringing anyone onto a project, not just interns. I actually went to a school that required every student in m

That overhead you're speaking of is present with bringing anyone onto a project, not just interns. I actually went to a school that required every student in my program to do a minimum of 1 year of paid internships (split into 3 and 6 month blocks). Judging by how abundant and competitive the companies looking for interns were I'd say they found it very much worth the overhead.