And the beat goes...off

According to most research I've read, creating a habit takes 21 consecutive days.
21 consecutive days of me getting up and exercising, for example (and let us keep in mind that THAT is a purely hypothetical example), would mean that I am now in the habit of exercising daily.

It should follow then, that getting kids in the habit of waking up at a particular time, would take 21 consecutive days of waking them up at that time. After which they will be in the habit of waking up at said time, and will then consistently do so.

Anecdotally, however, my experience differs from the research; anecdotally my experience shows that it takes around 15 weeks (105 days) before the waking-up-on-time habit kicks in for school age children. In other words, just about the time that winter break rolls around, we've gotten in the habit of waking up on time.

This leads me to believe that circadian rhythms are not subject to the rules which govern habits.

The proof of this is weighed out when looking at the reverse: although the majority of research I've read on the subject agrees that it takes at least as long to BREAK a habit as it does to create one, it does not take 15 weeks for the kids to get out of the habit of waking up on time. It only takes one...day.