NOAA
Noaa: Be a Tree Ring Detective [Pdf]
Discover the reason why trees have rings. Then use your skills of inquiry to decide which tree samples are the oldest, based on their rings.
PBS
Pbs Teachers: Methuselah Tree
Examine how scientists determine the age of living and non-living trees and identify factors that impact sizes of tree rings. Analyze tree ring samples and determine the age of the oldest sample.