When your normally sweet, well-mannered child starts acting out, mouthing off, or otherwise whining about stuff that usually goes unnoticed, you probably have that little warning light flashing in your head that says tonight should be an early bedtime (definitely for him, maybe for both of you). Here are four other signs of sleep deprivation in your child.

1. They’re hyper and unfocused.

These are the classic signs of an over-stimulated, under-rested child. “All kids have different sleep needs, but they still exhibit the same behavioral changes when they get overtired,” says Lisa Meltzer, Ph.D., associate professor of pediatrics at National Jewish Health in Denver, Colorado. “If your child is acting especially hyper, that’s a clear indications that he didn’t get enough sleep.”

2. It takes more than 15 minutes to get them going.

While there will always be morning birds and night owls, all kids who are well-rested should be able to get up and get going within 15 minutes of their morning wake-up. “It’s best if kids can wake up spontaneously, but regardless, those with enough rest will be able to get themselves going quickly, while sleep deprived kids seem to drag and drag,” says Meltzer.

3. They oversleep by two hours or more.

For school-age kids, weekday wake-ups are determined by the need to make it to class on time. But on the weekends, for 6- to 10-year-olds, if your kid is sleeping two or more hours past the weekday wake-up time, it’s a sign she should be getting more rest during the week (“teenagers are a whole other ballgame,” says Meltzer).

4. They fall asleep in odd spots.

If your child rapidly dozes off on the school bus, at a friend’s birthday party, or during a sports event, that’s a sign they’re not getting sufficient rest, says Meltzer. While it’s natural to fall asleep during a soothing movie or a smooth ride in the car, sleeping in environments that are noisy and stimulating means your child needs more quality sleep at night.