Occupational therapy practitioners (OTP) work with individuals with diagnoses that are subject to stigma including attention-deficit hyperactivity disorder (ADHD). While measures have been developed to broadly assess implicit attitudes toward disability, bias toward ADHD specifically has not been examined in individuals who work with this population. This cross-sectional study involved school-based professionals recruited via online message boards. Forty-seven individuals (24 OT, 23 other professionals) participated in online questionnaires including the ADHD Stigma Questionnaire to assess explicit bias. An author developed Implicit Relational Assessment Procedure focusing on stigma words related to ADHD was completed by a subset of 27 individuals. Although both groups displayed bias, occupational therapy practitioners demonstrated lower rates of both explicit and implicit bias toward individuals with ADHD than other professionals. Correlations between lower explicit and implicit bias scores were found among all participants. This study introduces an important tool for assessing preexisting biases toward children with ADHD. It has the potential to impact educational training regarding diversity, equity, and inclusion for professionals working in the school and early intervention setting including occupational therapy practitioners.