Many people have asked about doing a dual monitor setup on their own computers. For the computers in the classroom with dual monitors, these computers have two distinct video cards installed that allows us to perform this trick. The secondary video card can be used to mirror the primary display or act as an extended display.
Depending upon your own hardware, this option might not be feasible or affordable. However, there are a few relatively inexpensive apps that can help you achieve a similar setup with an iPad or Android Tablet.
Check out this article from Yahoo on two apps, MaxiVista and AirDisplay that will let you use the devices as a secondary monitor.