We present multi-color light curves for the W UMa-type eclipsing binary TU Boo for two epochs separated by 22 years .
An analysis of the O-C diagram indicates the earlier observations took place right in the middle of a major period change , thus allowing for a unique study on mass transfer and period changes in this W UMa-type system .
We compute model fits to our light curves , along with the only other published set , using the Wilson-Devinney program , and find temporally correlated changes in the size of the secondary component with anomalies in the O-C diagram .
We investigate the cause of these changes and find support for the existence of rapid , large-scale mass transfer between the components .
We postulate that this interaction allows them to maintain nearly equal surface temperatures despite having achieved only marginal contact .
We also find support for the evolutionary scenario in which TU Boo has undergone a mass ratio reversal in the past due to large-scale mass transfer so that what is presently the secondary component of TU Boo is in an advanced evolutionary state , oversized due to a helium-enriched core , with a total system age of \geq 10 Gyr .