SPOILERS
An interesting episode - while the first act was slow and took a while to set up the plot, the second and third acts were very well done, with full of laughs.
It was nice to see more of the interaction between Bobby and Kahn Jr (last we saw of this was back in Plastic White Female), as well as where John fits between the two of them. It was also nice to see the rivalry between Hank and Kahn (Sr.) developed more, as well as that there were still snippy to each other even during the rescue (Too many sitcoms would have had the two best of friends in no time). I would have liked to see more interaction between Peggy and Mrs. Kahn (name slips my mind), but we can save the Hill/Kahn battles for another episode :-).
I did like how the rivalry was relit, with the music professor igniting the fuse. However, the main slow point and rather bland section of the episode was getting the kids punishments started, and getting them to the cave. Once inside and to "The Boneyard" (in 'Ancient English' ;-), the episode moved at a good pace, with a good combination of the characters bickering at each other and the tension to save the children before it was "too late".
Though not KotH's strongest outing, this is still a good episode. Requires a bit of background on the Kahn/Hill story, but is good for a faithful watching. Grade: 9/10, or a A-.