Meet the Psychologists
Dr. David J. Lillenstein, NCSP
School Psychologist - Grades 9-12, Gifted
Dr. David Lillenstein has worked for the Derry Township School District in Hershey, PA since 2002. Dr. Lillenstein holds a bachelors degree in Psychology from the State University of New York - College at Buffalo, a Master’s degree in Educational Psychology from Indiana University of Pennsylvania, and in 2002 he completed his Doctorate in School Psychology at Indiana University of Pennsylvania, where he specialized in family-school relations. He is certified in Pennsylvania as a School Psychologist and Supervisor of School Psychological Services and has also earned the distinction of “Nationally Certified School Psychologist” (NCSP), and Model School Psychology Intern Supervisor by the National Association of School Psychologists. In 2019, he was awarded an Impact Award and the 2019 Alumni Scholar Award by the IUP College of Education and Communications for his contributions to the field of school psychology. Dr. Lillenstein was named the 2023 Government and Professional Relations Outstanding Advocate by the National Association of School Psychologists and was recognized in 2023 by the Pennsylvania Psychological Association. For Distinguished Contributions to School Psychology. Dr. Lillenstein has been actively involved in the Association of School Psychologists of Pennsylvania as President (2015-2020), PPA Liaison (2006-present), and Conference Chair (2010-present), and he is currently the Pennsylvania Delegate to the National Association of School Psychologists and the DPS School Psychology Section President with the Pennsylvania State Education Association (PSEA). Prior to Derry Township, Dr. Lillenstein worked for two years (1994-1996) as a school psychologist in East Stroudsburg Area School District as an employee of the Colonial Intermediate Unit #20, as well as for six years (1996-2002) with the Mechanicsburg Area School District. Dr. Lillenstein lives in Mt. Gretna, PA with his wife, Tiffany, and children, Sadie, Keara, Emma, and Benjamin.
Amanda B. Valentine, M.S., NCSP
School Psychologist - Grades 6-8
Contact Amanda Valentine
Amanda Valentine is a Nationally Certified School Psychologist with 20 + years in education and mental health. She has served the students and families of Derry Township School District in the roles of Learning Facilitator at the Early Childhood Center, Special Education Consultant at the Middle School and School Psychologist at the Primary and Intermediate Elementary Schools. Ms. Valentine holds a certificate in Educational Leadership from Penn State University. Areas of interest include assessment and programming for students on the Autism spectrum, school-wide positive behavior supports, parent-community engagement, trauma informed care and fostering growth mindset in students and teachers. Ms. Valentine is a trainer for Safe Crisis Management. She has provided professional learning and community presentations on topics such as disability awareness, mindfulness, effective collaboration, creating successful learning environments for students on the Autism spectrum, mental health, and anxiety in the classroom. Ms. Valentine resides in Hershey with her partner and two sons, as well as a very loving Golden Retriever.
Sara Wendell, Ed.S, NCSP
School Psychologist - Grades K-2
Contact Sara Wendell
Ms. Sara Wendell, Ed.S., NCSP, is a nationally certified school psychologist who joined the Derry Township School District in 2025. She earned a Bachelor's degree in Psychology from the State University of New York at Geneseo. She earned her Master’s of Education and Educational Specialist degrees from Lehigh University in 2023. During her graduate training, she was actively involved in work focused on the Response to Intervention (RTI) model for Specific Learning Disability (SLD) determination, rate of improvement metrics, early math skill development, and social emotional learning (SEL).
Prior to joining Derry Township, Ms. Wendell began her career at the Eastern Lancaster County School District. Her work emphasizes data-driven practices within Multi-Tiered Systems of Support (MTSS), Positive Behavioral Interventions and Supports (PBIS), and SEL.
She has presented at local, state, and national conferences on topics including SEL, MTSS, PBIS, and RTI. In addition to her school-based work, Ms. Wendell serves on the Association of School Psychologists of PA Communications Committee, and the National Association of School Psychologists (NASP) Professional Policy, Advocacy, and Credentialing Committee, where she contributes to advancing policy and best practices in the field of school psychology. Ms. Wendell resides in Hummelstown, PA.
Dr. Mike Valle, NCSP
School Psychologist - Grades 3-5
Dr. Mike Valle is a licensed psychologist and a Nationally Certified School Psychologist who joined the Derry Township School District in 2025. He earned a Bachelor’s degree in psychology from the University of Notre Dame and his Master’s and Doctoral degrees in School Psychology from the University of South Carolina. Mike has over twenty years of professional experience in public and private education and has expertise in trauma informed care, social emotional learning, crisis intervention, strength-based interventions, and Multi-Tiered Systems of Support (MTSS).
In addition to school-based work, Dr. Valle has worked in clinical private practice and has taught undergraduate and graduate level classes at Elizabethtown College, Philadelphia College of Osteopathic Medicine, and Lebanon Valley College. He has a specific clinical interest in helping athletes and teams overcome challenges and maximize their potential. Dr. Valle has also served as a certified Child Abuse Prevention trainer for the PA Family Support Alliance.
Dr. Valle is a member of local and national psychological organizations and is committed to increased access to mental health resources for children and families. He resides in Palmyra, PA with his wife and three children.