I don’t believe that I ever learned sentences like this to help with the spelling of words. I did learn things like Roy G. Biv, Every Good Boy Does Fine, Good Boys Do Fine Always (that’s the lines of the bass clef staff), and so forth, but that’s a bit different in my mind.
That “the principal is your pal” thing caused me more errors than it solved, because I internalized it that only the top administrator of a school has the -pal ending, and all other uses should be -ple. This leads to errors like writing about “the principle rule” or “the principle source of information.” Teachers everywhere, I beg of you: Stop saying “The principal is your pal.”
I assume you mean the “D,” as, in my dialect and most (if not all) of the American ones I’ve heard, the “D” is not pronounced at all, while the “N” is heard. Yeah, that’s one that I always say as “WED-nes-day” to myself when I’m writing or typing it out.
(Actually, is the “D” pronounced in any English dialects currently? I can’t seem to think of any offhand.)
I could never remember whether the second vowel in “separate” was an “a” or an “e” until I figured out that I could break them into three separate Spanish words. So in my head, it’s always “se para te.” Which doesn’t make any sense as a sentence, but I always spell it right, now.
My 12th grade teacher told us that she had difficulty remembering the order of presidents from Fillmore to Lincoln, so she made up the mnemonic device “funky peanut butter lover.”
And I’m sure most everyone remembers “please excuse my dear Aunt Sally” for order of operations and “kings play chess on fat girls’ stomachs” for taxonomy order.
On a side note, that reminds me of the old riddle about which two pairs of consecutive months have 31 days. July-August everyone gets, but the other?
December-January. People are generally not used to thinking of them as consecutive in this manner, what with one being in one year and the other in the next.