Only 8.7% of the students who took the Advanced Placement (AP) Physics 1 test earlier this school year scored a perfect 5, and Derry Area High School senior David McElfresh was one of them. He also finished in the 19% of the students who scored a perfect 5 in the Calculus AB test. âWe are very proud of him,â said Jennifer Welty, a teacher in the Derry Area School Districtâs gifted supports program. McElfresh, 17, the son of Michael and Kim McElfresh of Derry Borough, has been an honor student all through school. He took five AP classes last year, and he is currently taking four.