The first shift occurs around the time a child enters puberty (typically 11-13):
- Early Morning preferences become Late Morning or Afternoon preferences
- Late Morning preferences become Afternoon or Evening preferences.
The second shift occurs later in life, any time between 22 and 40:
- Evening preferences become Afternoon preferences
- Afternoon preferences become Late Morning preferences.
We have scientific backing, too! Research reports in the medical journal Pediatrics (2005) quote scientific evidence of a biological reason: teenage sleep rhythm actually becomes different between the age 13 and 22. The change means that a teenager's performance and achievement peak in the afternoon.