ReadWorks is committed to solving America’s reading comprehension crisis and student achievement gap. Driven by cognitive science research, ReadWorks creates world-class content, teacher guidance, and integrated tools that improve teacher effectiveness and student achievement. ReadWorks has an entire section just for Science available for all grade/reading levels.
Wonderopolis is a great source for encouraging thinking. You can search content or skim through all topics.
PlantingScience is a free online resource to teachers and schools. The program provides volunteer scientists, resources, and activities to support innovation in teaching, learning, and mentoring. Open education resources are shared for student-centered plant investigations that integrate scientific practices and big ideas in biology that meet the guidelines in the Next Generation Science Standards and other 21st century education standards.
We are a learning community where scientists provide online mentorship to student teams as they design and think through their own inquiry projects. The program is collaborative engagement in science education that crosses traditional learning settings: K-12 and higher education; learning in and out of class; hands-on and technology-enhanced.