Actually, they're "spelling tricks," but one of the 2nd-graders came up with the alternate pronunciation, and I like it.
N, tired from a full day of school and just after reviewing other spelling turkeys, when asked when you use "ck" for the (k) sound at the end of a word: "(tired pause)...After a bunch of other letters."
A 3rd-grader, practicing doubling the last consonant in some words before adding a suffix that begins with a vowel - I gave them the base word "rap." "Miss Kerri, is this right?" He had written "raped". I said, "No, that's..." and fortunately that's when my brain kicked in - "Erase the ed and start again; what do you do before adding the suffix?" "Oh yeah."
Teaching the letter x: after saying and having my 1st-graders echo several words that end in x, including "six", it was time to discover what letter was making that final sound - I asked the students to repeat the words we'd said earlier so I could write them on the board. One boy said, "Sex?" Silence, as I work on keeping a straight face and wait to see if he/they knew what the word meant. Soon the room was full of giggles - somebody's gotta' bottle that sound and give it away.