Many families struggle to pay college expenses for one or two kids. Certified financial planner Sarah Carlson, mother of two sets of twins, will soon have all four of her children in college at the same time.

The older twins are already there, to be joined soon by the younger two. But years ago, Carlson started teaching her children how to get an affordable education. One of the first steps was making clear what she would contribute.

“I let them know early on what I was comfortable spending and what I wasn’t,” says Carlson, who’s based in Spokane, Washington.

In my latest for the Associated Press, why you need to teach your teen about college costs long before the first application essay is written.