I am a preservice teacehr at the University of Northern Iowa. One curriculum that I have worked with and really like is FOSS (Full Option Science System). This curriculum is created for grades K-8. With this curriculum you can get access to online textbooks and teacher books. There are also lab kits that come with the curriculum that could help rural schools that may have limited resources. I know that FOSS is a full curriculum, and it also aligns with NGSS directly. FOSS is definitely worth a look! Good Luck!