Raising children and financial windfall aren't compatible concepts. But a few critical milestones involving school-age kids do put real money back in your pocket.

A big one is when your child starts a full day of school (assuming you’re using a public school and not merely transferring the cost of child care or nursery to the payment of private school tuition). Another is when your child feels secure enough to stay home alone without a babysitter. Age on this will vary depending on individual circumstances.

I ran into a friend the other day who was rejoicing over the windfall effect now that her second son is in full-time kindergarten. Both she and her husband hold down professional careers. He travels a lot. The $1,100 per month that had gone to nursery school she now plans to redirect to a 529 College Savings Plan.

I’m impressed by that level of discipline because I’ve been to her suburban home and know key rooms remain unfurnished even 7 years after they moved in. Their lack of ostentation is now even trendy!

I still recall my full-day kindergarten windfall way back when. It shifted from nursery school tuition to helping pay for my divorce.

This year I’m taking advantage of the second milestone - the child who is ready to stay home alone.

My daughter just started sixth grade and I was really counting on eliminating the $10 an hour babysitting bridge between the end of her afterschool program and my arrival home from work. (I know. I know. Many kids are forced to stay home alone or camp out at the public library because their parents lack the luxury of a financial choice in the matter.)

We gave it a trial run during the waning days of summer when all the scheduled camps and vacation had ended. Apart from a bit too much Disney Channel blaring in the background whenever I called, it worked fine. She passed my test as well as her own.

I’ve earmarked a laundry list of home repairs that will consume this small windfall. And let’s get real here: The older a kid gets, the higher the expenses seem to go for extracurriculars - sports equipment, singing lessons and the like.

But for just a moment, it’s nice to savor the year when back to school feels a little bit like back to solvency.

How did you invest the money from your own windfall? Weigh in on The Exchange.