By far, my toughest parenting challenge to date (and that is saying something, since there have been a whole host of them) was potty-training my older son. At the time, I had no idea that he was on the spectrum - I just knew that he was a little "different." I tried every tactic I read about, his pediatrician got involved (he was experiencing medical consequences from refusing to poop at all), I spent hours crying (not that that helped, but I just felt so helpless and like such a failure at parenting), and I prayed, and prayed, and prayed some more.
Ultimately, a year and a half into this nightmare, I did a St. Jude Novena that my parish was offering - nine days of Masses with that as my intention. I think God finally took pity on me. About a month and a half later, at the age of three and eight months, he woke up one day and started using the potty and never looked back.
I know compared to many children on the spectrum, that wasn't old at all. But once again, this was my first child and I didn't know that he was on the spectrum, and I was trying desperately to succeed at parenting, and the whole experience was not one I would ever want to repeat.
Thankfully, for those who do know that their child is on the spectrum, there are resources and strategies available. I came across this helpful article today: Potty Training the Autistic Child.