This would be a really cute idea for a teacher, except I'd probably get a jar at the beginning of the school year and have the kids write a little note every time the Teacher did something with or for them that they really appreciated, then they can present it to the Teacher at the end of the year.
I made these flowers as a goodbye gift for the 5th graders I was student teaching! I got all these materials at the dollar store: foam for the petals, star stickers for the stigma, glow sticks for the stem, tagboard for the leaves, and plastic goody bags to hold the smarties. (The petals read: "You are a class of Smarties - I enjoyed watching you grow! This flower is to remind you that you are a star! Good luck at the Middle School next year... SHINE BRIGHT!" The students loved them <3