Purdue with their emphasis on engineering will tend to weed-out students in calc & chemistry - unnecessarily. I would go with IU
Do not ignore this advice. Engineering schools (colleges known for their engineering emphasis) are USUALLY a terrible place to go if he wants to be competitive for medical school (or for admittance to other professional doctorates in the health sciences) I would have to be convinced beyond a doubt that somehow Purdue is different. Not to put down Purdue. Purdue is a marvelous school and your son would be lucky to go there. I frankly don't understand your issue with "he could get into a better school" I'm not that sure, maybe slightly better but that's not worth focusing on. The grass is always greener, I know.