In Exploring Magnetism, from NASA and the Center for Science Education at the University of California at Berkeley, students act as scientists as they discover magnetic fields and electromagnetism through inquiry and measurement. The unit includes complete lesson plans designed for students in 5th grade and up.
You'll want to explore the Utah Education Network's collection of complete lesson plans teaching magnetic behavior and earth's magnetic field. In one lesson, students use GPS to find magnets. In another, students compare permanent magnets and electromagnets. Independent students may enjoy exploring the Sci-berText on their own.
NASA introduces students to the earth's magnetosphere with this background essay. Scroll down to the Classroom Activities section for excellent lessons and explorations organized by grade level.
Exploring the Earth's Magnetic Field is a great classroom resource from NASA. It includes 23 activities for K-12 teachers to help you teach the basics of magnetism and Earth's magnetic field, with varying degrees of detail depending on grade level.
The study of Magnetism lends itself well to experiments and hands-on exploration. Try some of these experiments with your students and encourage them to make predictions, investigate, and draw conclusions.
Magnetic fruit? Magnetic free fall? These suggested activities from the Exploratorium will captivate young learners.
Money in a Blender, Magnetic Slime, and Newton's Nightmare. Students will be actively engaged with these cool magnet experiments, designed to interest even reluctant learners.
Magnet Man has compiled 80 experiments for primary grades through high school, featuring magnetic fields, levitation, electromagnets and more. The site also includes good explanations of the science behind the experiments.