For me sight reading was really hard at first, as I'm sure it is for all beginners. I remember in 6th grade I couldn't count rhythms well, but for me playing songs that were semi-familiar helped a lot. When I started playing, it was all about having fun and I played a lot of easy music out of a Beatles book. After a while I started taking lessons and my teacher made me learn scales. I still had problems with rhythms, but I started playing harder music and in 8th grade I got put into jazz band. After having to cover a part by myself for the first time my sight reading improve drastically. Now at my school, I am one of the stronger sight readers in the band. I think a lot of it has to do with learning scales young and playing music that I was familiar with (and easy) and gradually moving beyond what I was capable of playing.
-Weedy