In the book Literature Based Mini Lessons to Teach Decoding and Word Recognition, Susan Lunsford (a teacher) shares her enthusiasm for children's literature and describes various related teaching activities.

Following is an example of an activity that she performed in her own classroom. Go ahead and try it yourself. Changing ‘Y’ to ‘I’: Using Finger Pencils to Teach Plurals

An important plural rule that requires some practice is:

When a word ends in y, the y changes to i before you add -es.

After reading Blueberries for Sal by Robert McCloskey, we discuss how difficult it would be to make a blueberry pie with just one blueberry or eat just one blueberry, and how disappointing it would be to go berry picking and find only one blueberry. I write We love blueberrys on the board and say, “This doesn't look right,” before explaining the change that occurs in words that end in the letter y. I chant “y changes to i before you add e-s” and invite the students to repeat the rule with me. On the board, I cross out the y, write i above the crossed out y, and add -es to the end of the word. While I write it on the board, the children copy the changes on a friend's back using “finger pencils.”

We do the same for strawberry, blackberry, cherry, kitty, and any other word ending in y that the children think of. Each time I write a word on the board, I invite the students to copy the word in a different way—in the air, on the floor, on their legs. We overdramatize the erasing of y to help commit this procedure to memory. I explain that with practice, erasers are not worn down as quickly, and they will soon automatically change y to i before adding -es.