Pastor Miller
Thank you for your question and welcome to ADHDCentral.com.
I am not sure if children with step-parents are more likely to be diagnosed with ADHD. However, according to an article on PsychCentral, parents of children with ADHD are almost twice as likely to get a divorce (by the time the child reaches the age of 8). Therefore, children with ADHD may be more likely to have step-parents.
I hope this helps.
Eileen