This project evaluates and seeks to validate the Emotional Reactivity Test (ERT) as a predictive tool to determine puppies’ careers as successful working dogs, for which a reliable test is crucial because training working dogs requires significant investments of time, money, and human resources. Training begins as early as eight weeks, and determining a dog's career suitability can take over a year. 22 dogs from the Penn Vet Working Dog Center were included in this study, including Labrador Retrievers and German Shepherds, to predict their suitability for roles in Urban Search and Rescue (USAR), Detection, and Research.  In an ERT, dogs’ startle reflexes are tested through the presentation of a series of novel stimuli – objects they have never encountered before. Puppies are presented with these stimuli at five different time points from eight weeks to 12 months. The ERT measures dogs' startle responses to these stimuli, aiming to predict long-term career success based on emotional reactivity and behavior. Preliminary results show variability in the ERT's predictive validity, particularly for USAR dogs, but sample size was small and additional data is needed. Furthermore, the study compares subjective live scoring with objective behavioral coding, aiming to validate the ERT's live-scoring system.