University of Oregon
Determining Properties of Stars
An excellent website detailing how a star's properties can be determined, and how these properties lead to the way a star is classified.
Other
National Optical Astronomy Observatory: Jewels of the Night
Using the Jewelbox Cluster, students determine the cluster's age based on measurements of its color and brightness.
NASA
Nasa: Imagine the Universe: How Big Is That Star
This 2-5 day lesson plan investigates the diameter, radius and mass among several stars in order to understand stellar behavior, particularly in a binary system.