Some of these websites might be a little beyond primary/secondary schools however I am sure there will be material here which, used selectively, could be productive in education.
Link 1: Astronomy Picture of the Day [Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer]
Link 2: NASA - Home
Link 3: ESA Communications Portal
Link 4: Space, Stars, Mars, Earth, Planets and More - NASA Jet Propulsion Laboratory
Link 5: http://sohowww.nascom.nasa.gov/
Link 6: HubbleSite -- Out of the ordinary...out of this world.
Link 7: Spitzer Space Telescope
Link 8: http://chandra.harvard.edu/
Link 9: http://saturn.jpl.nasa.gov/index.cfm
Link 10: http://voyager.jpl.nasa.gov/
Link 11: http://messenger.jhuapl.edu/
Link 12: http://antwrp.gsfc.nasa.gov/apod/astropix.html
Link 13: http://spaceweather.com/
Link 14: http://stereo.gsfc.nasa.gov/
Link 15: http://ngm.nationalgeographic.com/
Some great links here worth looking at.
Source of most links here: Tom’s Astronomy Blog Blog Archive Interesting Astronomy Links