A survey of individuals holding the Nationally Certiﬁed School Psychologist (NCSP) credential was conducted via the Internet to gather information regarding their measurement of treatment integrity in school-based interventions and their beliefs about its importance. A sample of 806 self-selected professionals holding the NCSP credential provided data about the extent to which they measure treatment integrity and the methods they used to measure it when developing interventions via one-to-one and group/team consultation. Results showed that 97.6% agreed that measurement of treatment integrity was a key factor to consider and to include when evaluating interventions and when using intervention data for special education eligibility decisions. Few, however,reportedregularlydocumentingitinone-to-one(only11.3%)orgroup/teamconsultation (only 1.9%). Recommendations for how school psychologists and other school staff can increase their measurement of treatment integrity in school-based interventions are offered. C 2008 Wiley Periodicals, Inc.