The Penn Vet Working Dog Center, in Philadelphia, Pennsylvania, is like any other school. The students arrive by 9 a.m. They spend the day learning from their teachers. They practice following directions. And they have gym class, in which they exercise and work to improve their balance and agility. The only difference is the students at this school are dogs. The canines are learning to use their keen sense of smell to search for missing people, bombs and even cancer.