After agreeing to host over 200 students on a daylong genetics field trip, the author needed an easy-to-prepare genetics experiment to accompany the DNA-necklace and gel-electrophoresis activities already planned. One of the student's mothers is a pediatric physician at the local hospital, and she suggested exploring genetic-disease screening performed on all newborns. The author developed this hands-on, simulated screen for the inherited disease phenylketonuria (PKU), which captivated both students and their teachers and proved successful with several groups of middle school students. Designed as an interactive demonstration of inherited traits, this simulated PKU screen connects real-life genetic testing with the expression of inherited traits and proteins from DNA. It can also be used to emphasize the importance of controls when performing a scientific experiment. Most importantly, the PKU screen simulation uses safe, readily available, inexpensive reagents that provide strong, rapid visual results to explore basic patterns of inheritance. (Contains 6 figures and 8 online resources.)