Just like the classic mens' haircut (also known as the "short back and sides") this classsic look for boys is clipper cut along the sides and nape sections and gradually builds to perhaps an inch in length at the top and forward crown.
The cut has remained a classic because it is easy to care for, comfortable during most seasons, and generally works for nearly all hair types.
This classic cut is characterized by the tapered perimeter along the sides (around the ears) and back (the nape section) of the head.
The tapering often goes "to the skin" in summer or simply is tapered to a blunt edge in cooler months. The taper graduates to an inch along the parietal ridge and in the top and crown sections.