Ted -

I agree, you would think Justin Kaplan would know better.  My dog-eared
Penguin copy happens to be my favorite, however, mainly because I love Dan
Beard's illustrations.  I was curious, though, so I did a little research
for us:

According to the Library of Congress catalogue, Penguin is the only edition
that uses this 'revised' title, except some 'Selections' anthologies,
specifically Octopus Books and Longmeadow Press.  There, they seem to
delight
in using "at."  Also, someone named Tim J. Kelly of Denver's Pioneer Drama
Club adapted the book for a children's play in 1983, changing the title as
Penguin did.

Interestingly enough, however, the trend goes even farther back to around
the time of CY's original publication.  When Harper's magazine reviewed the
book in 1890, the article was called "A Connecticut Yankee at the Court of
King Arthur."  (Harper's, vol. 80, no. 476, p. 319-322.)

It is interesting to compare the two titles, from an Old World/New World
standpoint, and also from a physical stance.  "In" seems to be an
Americanism; "at" court is more proper for Brits, and they should know.
I wonder if Twain chose his preposition purposefully here...

What do you think?

Beth