Last year, the room mom for my daughter's 2nd grade class, sent home a sealed note asking each child to write a thank you/appreciation letter to the teacher. She asked the children to take their time with it and give it some thought. She encouraged them to draw a picture and/or design the letter with a border. Each family also chipped in $5 a piece so that the room mom could present her with a gift too. (She asked that the children hand in the letter and $ donation to her daughter in a sealed envelope at school.)Then the children presented it to her a few days later on.
When I taught 1st grade, my room mom that year had each child put their thumb in paint and put their thumbprint on a large terra cotta pot. After that dried, she had them design their thumbprint into something. Most of the kids created animals from their thumbprint. She wrote their names in paint under each thumbprint design. Then around the rim of the plant she painted the sentence..... Thanks Mrs._____________ for helping us bloom!
Then she planted a beautiful plant in the pot. (I still have the pot today.....15 years later. So I'd say it's a keepsake:-)