Like Scratch, GameMaker is an introduction to programming; the difference is that Scratch is a free educational language, while GameMaker is proprietary and for-profit (the company’s home site is http://www.yoyogames.com/). GameMaker can be a powerful teaching tool, though, because it allows students to create computer games while learning basic programming techniques.
The Game Maker’s Apprentice: Game Development for Beginners (Apress, 2006), by Jacob Habgood, Phil Wilson, and Mark Overmars (the software developer) is a self-teaching guide.
The company’s home site (yoyogames.com) offers tutorials and projects.