It depends somewhat on what school he is attending and the type of firm he is shooting for. In my S’s summer intern class at a bulge bracket, there were many interns from the usual Ivy and LAC feeders that don’t have finance majors, other than Wharton. The other interns were typically from a business school of a good university (e.g. Stern, Ross, etc…). Part of the challenge is where and which IB’s are steered to initially in your S’s school. It’s useful to be on the “list” of students who are invited to “get to know you/networking events” that many IB’s host at the schools.