Objective: Whether and to what extent racial/ethnic disparities in attention-deficit/hyperactivity disorder (ADHD) diagnosis occur across early and middle childhood is currently unknown. We examined the over-time dynamics of race/ethnic disparities in diagnosis from kindergarten to eighth grade and disparities in treatment in fifth and eighth grade. Methods: Analyses of the nationally representative Early Childhood Longitudinal Study, Kindergarten Class of 1998-1999 (N = 17 100) using discrete-time hazard modeling. Results: Minority children were less likely than white children to receive an ADHD diagnosis. With time-invariant and -varying confounding factors statistically controlled the odds of ADHD diagnosis for African Americans, Hispanics, and children of other races/ethnicities were 69% (95% confidence interval [CI]: 60%-76%), 50% (95% CI: 34%-62%), and 46% (95% CI: 26%-61%) lower, respectively, than for whites. Factors increasing children's risk of an ADHD diagnosis included being a boy, being raised by an older mother, being raised in an English-speaking household, and engaging in externalizing problem behaviors. Factors decreasing children's risk of an ADHD diagnosis included engaging in learning-related behaviors (eg, being attentive), displaying greater academic achievement, and not having health insurance. Among children diagnosed with ADHD, racial/ethnic minorities were less likely than whites to be taking prescription medication for the disorder. Conclusions: Racial/ethnic disparities in ADHD diagnosis occur by kindergarten and continue until at least the end of eighth grade. Measured confounding factors do not explain racial/ethnic disparities in ADHD diagnosis and treatment. Culturally sensitive monitoring should be intensified to ensure that all children are appropriately screened, diagnosed, and treated for ADHD.