This is the Pendulum Clock from the LEGO Education Simple and Powered Machines Set. It can be used to demonstrate the variation of period with length of pendulum and is a very good visual representation of the escapement mechanism.
There are many other models that one can build using this set, including a weighing scale, elastic energy powered car, etc. All with potential for class demonstrations.
You can buy a set from Duck Learning in Singapore at (S$329.75), an exclusive distributor of LEGO Education products in Singapore. If you are purchasing in bulk for your school, you may want to contact them directly for a package deal. You can also purchase them from overseas sites such as Bricklink.com if you can find them at a better price.