Transitioning out of the blessed schedule of regular napping is awkward, at best. Confusing, maddening and sad also apply—especially when one of your children gives up her naps a good two years before your other one did. My expectations have been dashed. ---

It is unfair to expect my daughter to have the same sleep skills as my son. So, I'm easing my expectations by averaging their sleep habits. According to the National Sleep Foundation, "a child will spend 40 percent of his or her childhood asleep." This works in our family by factoring Theo's early years at about 60 percent sleep and Sylvia's at roughly 20 percent.

Theo's naps sometimes lasted three to four hours, and they ran for five good years. He knew when he needed one, and I can't recall him resisting the afternoon balm of his bed and a dim room. I felt like a supreme parent.

Sylvia has the capacity to take her siesta calmly. She also has the capacity to fight sleep in inverse proportion to her need for it. She does this often; I feel like a parental wreck.

For a long while, I fought for the nap: "It's time to sleep now," I said. "Your brain and your body need to rest to grow," I explained. "We'll go to the park after your nap," I bargained. "You MUST take a nap," I insisted. "Sylvia! GO TO SLEEP!" I yelled. She wiggled and flopped, talked and yelled back, got up and jumped around, left her room and skipped around the house.

I tried giving her more context: I had accounted for her napping at least an hour a day in my work scheduling, and her cooperation was imperative to effectively organizing my time and obligations. This left her unswayed.

We read, sing and cuddle, but Sylvia puts little stock in the benefits of repetitive ritual. She likes to mix it up: She sprawls atop the covers, balls up in a cave beneath them, moves onto her child's couch, puts the child's couch on top of her, wears her princess dress to bed, removes all clothing, jumps on the bed, jumps off the bed, checks the reflexes of her wall with the hammer from her doctor's kit.

Theo finds solace in sucking two fingers and stroking the plastic eyes of his stuffed monkey, Murphy. Sylvia lies down with different objects all the time: stuffed animals, baby dolls, plastic cups, balls of shredded Kleenex, rocks, shoes, jackets, and stacks of small Beatrix Potter books with their dust jackets removed.

I'm broadening my concept of "nap." Now, I'm okay if Sylvia just stays in her room for quiet time. The thing is, she's loud in there—lots of things bonking around, lots of dramatic narrative and operatic singing—so it's not quiet time. It's neither particularly productive thinking/working time for me, nor, from the sound of it, particularly restful time for her. So, why press the nap or, even, rest time?

Sylvia is 3, and many kids give up consistent naps at 3. Some do without them entirely. At the same time, naps help alleviate the whiny crankiness of late afternoon, they seem to extend my kids' emotional stamina, and they help rack up the 10-13 hours of sleep recommended for preschoolers and early school-aged children. Also, recent studies indicate naps help preschoolers' brains better process what they've been learning"

Science magazine online ran a story last month—"Naps Nurture Growing Brains"—about a recent study of the effects of preschoolers' naps on memory tests. The study, headed by University of Massachusetts psychologist Rebecca Spencer, "provides the first evidence that daytime sleep is critical for effective learning in young children."

The study's preschoolers performed notably better on memory-game tests after a nap, seemingly regardless of how much nighttime sleep they'd gotten. According to Spencer, "they need that sleep close to learning," for the new information to stick.

Aha! Parenting support registered: I would reinstate Sylvia's daily information-retention nap. But then, the study suggested that napping's memory benefits diminished for children who no longer took a regular nap—that certain kids' brains no longer needed mid-day sleep and could handle being awake for a longer period.

Sylvia naps at preschool, but she doesn't much at home. That's this week's reasonable split. But what to do when Sylvia's hour of wall-pounding, floor-thumping quiet time turns into a nap at the very end of the naptime, five minutes before we need to leave for something?

The other day, she spent her quiet time removing all her books and toys from her bookshelves. She apparently did this so that she could sleep on a shelf, which is where we found her. Wake her up? Or "never wake a sleeping child" and deal with the won't-sleep-at-night consequences later?

These questions keep me awake at night, which means I need to start napping. I must be in good company, even among non-parents: The CDC says "insufficient sleep is a public health epidemic," and The Wall Street Journal published a handy graphic tagged "Field Guide to the Perfect Nap." Some studies have suggested that napping is correlated with cardiovascular health. Most people agree that short "power naps" can boost mood and alertness.

Just last week, Science online ran a piece about the possible brain-cleaning function of sleep that "clears the brain of toxic metabolic byproducts." A while back, RadioLab ran a show that discussed sleep as a cleaner-upper of clumping cellular proteins (clumps are bad) and as a series of electric waves that wash over the brain and soften the mess of information we accumulate while we're awake.

So maybe napping is a little quick-cleaning fix—like picking up a room without vacuuming, or folding the laundry without putting it away.

Whatever the analogy, I was in desperate need of a nap the other day. I'd stayed up too late the night before reading about, what else?—sleep! I went to bed only after I'd found this quote from Cervantes' Don Quixote: "Finally, from so little sleeping and so much reading, his brain dried up and he went completely out of his mind." I slept for a couple hours until Sylvia screamed in despair over not being able to find one of the tap shoes with which she was sleeping. Shortly thereafter the alarm went off.

Later that day—at NAP time—she didn't buy the nap science. I tried lying down with her in napping solidarity, but then she just kept me awake. "Fine," I said. "You just stay awake, and I'll go into my room to take a nap." I went. She followed. I groaned. She climbed into bed with me and let me fold myself around her cozy (and momentarily still!) body for a delicious little afternoon brain cleaning. Three minutes later, it was time to go get Theo from school. He needed to come home for a nap.