Among those to have taken action to side-step the lengthy wait are Jannine and Chris from Halifax.
The couple were told it could take up to two years before their children, Oliver, 13, and Sophie, eight, would be seen by the NHS in West Yorkshire.
"Oliver's ADHD was debilitating," said Jannine.
"For both children, ADHD manifested itself through anxiety, being unable to focus on their education, and emotional dysregulation.
"Oliver couldn't face going to school because of the anxiety. Sophie, especially on a Monday, would come home just completely burnt out. We were just banging our heads against the wall with the NHS."
After making the decision to go private, the couple paid more than £8,000 for assessments which led diagnoses for both children and now pay a further £500 each month for their medication.