I read this book in school maybe 4th or 5th grade. What I remember is it was another planet, maybe a moon and the people had put up a series of watchtowers or light houses or something. IIRC a kid took over one of the towers because something happened to his dad who was supposed to be controlling the tower.

Anyone have any ideas? The word sentinel seems to stick out about it for me but I've tried google and cant find anything.

Cross posted to GD .