Having been a parent for 20 years, I figured I understood child-rearing. But no. Not since I’ve entered a new phase of parenting.

Any mom or dad who raised a teenager knows this universal truth: about age 16, commensurate with driving privileges, the teenager instantly acquires Dumbledorian wisdom and insight. Almost like magic, he can expose human foibles as easily as shining a flashlight, and when that powerful beam illuminates us parents, we see our weaknesses in stark relief. How eye-opening to learn that, after so many years, we’ve been doing everything wrong — driving, dressing, purchasing, cooking. We don’t know how to manage our careers, our finances or the relationships in our lives. Heck, we can’t even pick a good movie or play a good song on the stereo. Sobering but true.

Mark Twain wrote, “When I was a boy of 14, my father was so ignorant I could hardly stand to have the old man around. But when I got to be 21, I was astonished at how much he had learned in seven years.” Some say Twain wrote tongue-in-cheek, but surely teenagers take him literally. After all, parents are screw-ups. I know I am.

My parenting choices have been wrong all along, as I’ve learned in this new phase, now that some of my kids have become tenured professors of life.

Only parents with multiple kids whose ages span a decade or more can receive this blessing. My older kids are ready, willing and able to critique how I’m raising the younger kids, ages 11 and 8. The child becomes teacher, and the parent becomes student.

Here’s an example. One of my teenagers helped me understand that I’ve mismanaged computer game use. One evening, the 11-year-old was glassy-eyed from staring at Minecraft when the teenager offered valuable insight. “Remember, Dad, when I was his age and wanted Runescape and you said no, so I asked again and you said no, so I pushed harder and then you said yes?” I nodded, remembering with shame. “Well, that was a mistake,” he said, stealing a Camaro in Grand Theft Auto V, “and you shouldn’t make the same mistake with the little kids.”

A different teenager helped me understand my slip-ups regarding eating habits. The other night, when the 8-year-old reached for a second cupcake, my teenage daughter astutely spotted a learning moment. “Dad, when I was his age, I nagged you constantly for sweets until you gave in. Well, that was a mistake,” she said, sculpting the Cool Whip on her third wedge of pumpkin pie, “and you shouldn’t make the same mistake with the little kids.”

Such harsh lessons can be difficult to take, so I sought reassurance with a trusted confidant, my dad.

“Kids these days seem so entitled,” I said. “Was I like that?” I thought a moment. “There was that time I really wanted a BB gun but you said no. Remember that?”

“How could I forget?” he said, taking a slow sip of scotch.

“I pushed and pushed until you finally let me get it.”

Dad smiled warmly at the recollection.

“Well, that was a mistake,” I said, frowning. “If you hadn’t done that, I would’ve learned my lesson and become a better parent, and my kids wouldn’t be so screwed up today.”