Sorry if this has been done to death before 
DD1 is 12 and goes upstairs to shower at 8, in bed by 8.30 and allowed to read until about 9.
She's fine with this but was saying a lot of girls in her year (7) are up until 10/10.30, and one even 11.30!
Just interested to know what time your 11-13 year olds go to bed at thanks 