I am always collecting shells from the beach with my girls. When we go on holiday the girls always come home with a bucket full of shells.
Last year in class I took the shells in and got students to choose a shell to sketch.
This year I decided I wanted to make a zen garden to place in a quiet area in the classroom for a calming down strategy. Students can rearrange the shells or rake the sand and calm down whilst doing this. The thing I liked about this most is it doesn't make noise (bonus).
To make a zen garden I brought a photo frame from a discount store. I then removed the glass and used electric tape to tape the base to the frame. I then turned the frame over and filled it with sand collected from the beach. I let my girls place some shells and drift wood on the sand. Completed. Easy enough for all students to make. Give it a go and feel free to let me know how it goes in your classroom.