Mergent Historical Securities API
From http://www.programmableableweb.com:
Provides historical quotes for all US and Canadian stocks, indices, mutual funds, OTC bulletin board issues, and other securities. Prices are fully adjusted for splits, dividends and other corporate actions. Data on both living and dead issues is available. The API also provides access to non-price data such as short interest, shares outstanding, earnings per share and more.
This API along with one of the news archives could make an interesting exercise for high school or even college students.
What news events affect stock prices?
Do events of the same nature have the same impact?