Nyal Williams wrote:
Properly done, boxing the wake begins by a descent
through the wake, a box around the wake, and then an
ascent back up through the wake. This shows the student
the extremes of where one can go safely on tow.

I agree and this is how I do it and teach it. But in the US, the PTS
doesn't say that you have to do it this way. And, it's referenced source
for the maneuver, The Soaring Flight Manual, also does not mention going
through the wake. If, on a flight review, a rated pilot boxes the wake
without going through it, I keep my mouth shut. But, then later I will
ask for a tow transition through the wake prior to release.

Tony V
http://home.comcast.net/~verhulst/SOARING