Upon joining the faculty at Indiana University, Clapp was one of the first faculty recruited to join the
Herman B Wells Center For Research in 1991. In 2008, Clapp and colleagues discovered that the drug Gleevec had the possibility to be the first effective therapy for neurofibromatosis type 1 tumor. Following this, Clapp was named the Chairman of the IU Pediatrics Department while continuing to serve as the Freida and Albrecht Kipp Professor of Pediatrics and a professor of microbiology and immunology. In this role, he oversaw the establishment of a national research project to develop new treatments for diseases of a genetic mutation. In October 2020, Clapp was elected a Member of the
National Academy of Medicine for "work that has led to fundamental new insights into the pathogenesis of neurofibromatosis and improved lives for children and adults with this disorder." He was also awarded the Children’s Tumor Foundation's Friedrich von Recklinghausen Award as someone who has made significant contributions to neurofibromatosis research or clinical care. In 2021, Clapp was one of 11 IU faculty members named distinguished professors. ==Personal life==