Snap! is a site that is ideal for MS/HS learning how to program. The site is a spin-off of Scratch and works very similarly w/ a drag-n-drop interface of "snapping" pieces of blocks together. These blocks are commands and a user can see on the right side of the screen what is happening as they put these blocks together.
I recommend checking out Snap! by clicking here!!!
For a more detailed review check out Free Technology 4 Teachers.