The CERES Project: Educational Activities site provides resources for educators in grades K-12. There are 28 lessons, from studying the movement of celestial objects to exploring how organisms adapt to their environments through changes in their genetic codes.
The lessons are categorized by grade level. You can see the grade levels listed on the left side of the screen. In addition to the grade levels, there are clock icons that indicate how long the lesson should take and NASA theme icons, which represent four themes: Structure and Evolution of the Universe; Exploration of the Solar System; The Search for Origins; and The Sun-Earth Connections.
You can use the classroom-ready lessons on this site to complement your units on space science and astronomy. All of the resources make use of the National Science Education Standards and provide a clear breakdown of learning outcomes as well as lists of any materials needed for the activities. They also provide the scientific background necessary for you to be able to carry out the activities with your students.