I only ask because until 2005, I had no idea it exsisted. If you have a child who attends a private school due to his or her severe learning disabilities or neurological disorders or behavioral/emotional/mental health issues, you can add the cost of tuition, transportation, and sometimes even books to your Medical claims on your Schedule A.
Until I learned of this option, I never had medical expenses that were more than 7.5% of my income. Add in the cost of one year of private school, and you'd be surprised how easily one is carried past that 7.5 % hurdle.
One caveat--a medical professional must "recommend" the private school for your child, and there must be a medical diagnosis regarding the child. For me, that was easy--I'd never heard of either the middle school nor the high school my youngest daughter wound up attending before her psychiatrist told me about them. But I don't think most pediatricians or therapists would mind a backwards recommendation once you tell them about the qualities of the school you've chosen for your impaired child.
If, like me, this deduction makes a significant difference on the Schedule A, then you also have the joy of filing amended returns and getting even more money back.
For more information check out this link, which, while written for last year's returns, is still good tax law, so far as I know.