Earth science is a course offered in American schools for 13-15 year old students. I can think of a few ideas off the cuff.
Get a good photograph of the Moon showing LOTS of craters and count how many craters you find in a range of diameter classes. Most of these craters were formed during the first billion years of the Moon's formation, so the frequency of craters you count can be related to the cratering time scale for that size range. Small craters are more frequent than large ones so the interval between small cratering events is just the number of those craters you count over the whole Moon, divided by 1 billion years. With this information, you could estimate the ages for some of the craters you find in which smaller craters are seen inside them.
Use the published rising and setting times reported in back issues of your local news paper to plot on a graph the seasonal changes in the rising and setting times for the Sun. Explain what the graph shows in terms of the orbit of the Earth and its changing speed around the Sun.
How often do Blue Moons occur? The time between Full Moon and the next Full Moon is 29.5306 days. If the next Blue Moon occurs on July 30, 1996 figure out when the last five and the next five will happen.
Get on the internet and call up some of the resources for images and data I have in my HOTLIST. Create your own catalog of astronomical sites related to specific topics you select. Ask astronomers how the various kinds of data are used. Go to one of the telescope sites and have a look at how to submit an observing proposal. Create one yourself by going through the process of 1) selecting a question to answer, 2) thinking about what observations you would need to answer the question, 3) the logistics of getting travel money and time to actually make the observation, 4) the different problems you could run up against in making your observation including bad weather which affects observations at different wavelengths to differing degrees.
Look at the Hubble Space Telescope observation archive and survey what kinds of things astronomers are looking into.
Contact a professional astronomer ( like me!) and get them to send you published data from different kinds of observatories. Ask the astronomer what kinds of questions could still be looked into with the data. We often don't have the time to track down every little thing that particular data suggests to us.