The clock change. What it actually does to children.

The circadian rhythm — the internal clock that regulates sleep, waking, appetite, hormone release, body temperature, and mood — runs on an approximately twenty-four-hour cycle that is anchored by external cues, primarily light. When the social clock shifts by an hour, the biological clock takes between five and seven days to adjust, during which time the two clocks are running in desynchrony. The child goes to bed at what their body believes is eight o'clock and wakes up at what their body believes is six, regardless of what the wall clock says.

The result of this desynchrony is a specific set of symptoms that parents describe as mood and behaviour but that are actually physiological: irritability, difficulty falling asleep, waking earlier than usual, reduced appetite in the morning, increased hunger in the afternoon, difficulty concentrating, and emotional reactivity that is out of proportion to the events that trigger it.

This is not misbehaviour. It is jet lag. Not metaphorical jet lag — literal jet lag, the same mechanism, the same physiology, differing only in whether the time zone changed or the clock did. The child's body is in a different time zone from the family's social schedule. The child's biology is in a different time zone from everyone else's schedule.