I got my AGI and IGI before I got the CFI and taught private, instrument, and commercial ground school with a commercial. We all start somewhere. In a perfect world you would be required to be an airline captain with 20 plus years of experience to get a CFI. And you'd have modern working equipment - not a beat up old 150.
Instructing makes you better because you discover that you better know the material. If this person is lacking to some degree,hopefully this first teaching experience will encourage him to hone his skills. I've also been a FL middle school teacher and I can tell you I'd rather shoot approaches all day at ORD to mins, than stand in front of 8th graders all day long. Teaching is a tough gig to begin with.