Tween stalling often looks like genuine wakefulness: they are not tired at bedtime because the circadian phase delay of puberty has pushed their natural sleep window later. Asking a tween to be asleep at 9pm may be biologically impossible for many of them. The stalling is partly the nervous system accurately reporting its state. This does not mean bedtime disappears, but it does mean the approach needs to account for the biology.
I know your brain feels awake right now. Let's get your body into the conditions for sleep and let the biology do the rest.