Scratch is a brilliant visual programming tools specifically targeted at getting students and novices involved in programming and makes it dead simple for them to create a game or multimedia presentation in next to no time.
I personally have introduced a lot of classes to SCRATCH and have found the best way to do this is is introduce show them some videos explaining what it is and what it does. Then have about 3 copies of the instruction cards printed and laminated to give to your students.
Once you have laminated cards they will show the kids how to do a specific task such as make an object follow the mouse, add music to a game or animate a sprite.
Each task takes bout 5 minutes and there is about 12 in all. I guarantee this will sow a seed in your students head and they will be making their own scratch apps and games in a jiffy.