In order to introduce linear perspective to 6th graders, I first give them a unit on architectural history and design. They each make a set of four drawings of either a small vacation home or a fast-food restaurant:
Once they have that experience I've found they're more motivated-- feeling a NEED to learn and understand linear perspective.
Start out with one-point perspective with the teacher using the overhead or whiteboard to draw. Art students will follow along with Drawing Pencils and 9x12 (22.9 x 30.5 cm) Drawing Paper. First students are introduced to art terms such as "horizon line" and "vanishing point." A simple rectangle is created with a pointed roof.
Once students have followed along and seem to have a grasp at basic perspective, students will then draw four separate drawings that include their dream vacation home, fast food restaurant, or any other building that peaks their interest.
"Michael Delahunt authors and publishes an online art dictionary called ArtLex. In addition to defining art terms, ArtLex offers thousands of images of examples, pronunciation notes, great quotations, and cross-references."
Perspective Without Pain - this book takes you through a step by step process geared toward all levels of drawing. The beginner is comfortable right away with this daunting subject and the advanced student hones his skills through the study of the later chapters.