Eight bright picture cards, each showing more than one of something, with the singular word and two circles: s or es. The child circles the ending that makes the word plural.
It isolates the one decision that trips first graders up, which ending to use, without asking for any spelling. A tip across the top reminds them that words ending in s, x, ch or sh take es.
Toothbrush, mailbox, princess and ostrich are the es words, and they are fun ones to say out loud. Hearing the extra syllable in toothbrushes and ostriches is the easiest way for a child to remember why the e is there.