S18 is doing a consulting internship (with a smaller specialist firm) this summer. They offer jobs to all successful interns and actually train them now alongside new joiners who weren’t interns, so it wouldn’t matter when you come back (and you have the option of working part time during senior year too).
So I’d be looking for an internship in that last summer with a company that he wants to work for after graduation so he can get any basic training in then. Most consulting training is on the job anyway, S only had 1 week of basic training on computer systems etc before starting billable work. His main takeaway so far is that Excel skills are all important.