What's a constructive way to guide a child who occasionally takes items from the classroom?

I am assuming that this child is under the age of 6. Often children love the materials so much they want to take them home, want to share them with their family. Firstly, there is never a punishment for such an activity. Talk with the parents, and explain that there is no punishment, but that you need the materials to be returned. Talk with all the children about the fact that sometimes they do love the materials so much they want to keep them.  Explain that when someone takes something, the remaining pieces of the material must be removed from the class, thereby eliminating the possibility of others using that material. This approach appeals to the highest nature of the child.  Generally, this is a short-lived situation.

Child's hand on Montessori materials