Using metal insets gives the students an opportunity to strengthen their eye hand coordination, fine motor and writing skills. As the students trace the insets they are learning how to properly hold a pencil and how to apply proper pressure when using a pencil. The student places a metal inset paper onto the tray and places the inset over the paper. They then trace the inset and color it in before removing inset. An extension to this work is to have the students write the name of the shape at the bottom of the page and then staple all the pages together to make a shape book.
Here you can see that the student colored in the shape and then labeled the shapes. When she was done she stapled the pages together.
This is how the metal insets are displayed on the shelf. We only have on set out at a time and we switch them periodically to help keep their interest in using them. We also show them how to use the different shapes to make things like Easter eggs, Christmas trees, flowers, balloons, etc.
The Montessori At Home With Love blog has some great info about metal insets http://montessori-in-the-home.blogspot.com/
Here is a link to a printout that you can use if you would like to make your own metal insets http://www.montessorimaterials.org/Language/metalInsets.pdf
Discovery Days and Montessori Moments also have some different ways to use the metal insets http://discoverydaysandmontessorimoments.blogspot.com/2012/01/montessori-essentials-metal-insets.html