The colourful building blocks a beloved by kids the world over. They have also been employed by primary schools teachers in an ad hoc manner in the classroom from time to time.
The Lego company has recently moved into the education sector with their MoreToMaths kits, which include lesson plans and teaching guides. Unfortunately the relatively steep price may deter many schools.
However, as you can read here, there are still creative ways to use standard Lego block creatively in the classroom.