[racket] Adding teachpack from Language menu?

The docs tell me in several places to load a teachpack with the
Language->Add Teachpack menu pane in Dr. Racket.  Unfortunately, my
Language menu does not contain an "Add Teachpack" item, the only item
it contains is "Choose Language ...".

Selecting this item brings up a dialog which includes a non-editable
field which is labeled "Teachpacks" and contains the text:

 (lib "convert.ss" "teachpack" "htdp")

Dr. Racket's Help->Check for Updates tells me I'm up-to-date.

The "convert.ss" module is one that I loaded, somehow, within the last
couple of days.

Please advise.

-jmc