The articles I've listed all contain information and analysis with implications for the question you posted. May I suggest that you consider using http://www.eric.ed.gov/ - an excellent resource for research on topics in education for any additional sources?
Much of the literature that supports exit examinations seems to assert many of the same principles. Value seems to be an overriding theme. The standardized approach to the exam helps to create a "value" to the high school diploma. This argument assumes that students have been promoted and "passed over" without a sense of understanding and focus which makes learning meaningful. This is followed with the idea that the exit exam makes a diploma "more valuable" because kids endured a standardized assessment in order to achieve it. Additionally, the streamlining of the curriculum and emphasis on essentialiaty is another element that is presen in the exist exam issue. Stuents are able to focus on what they have to know and the elements they need to know prior to leaving a specific grade level.
Try to find it on Sage Publication online. Here is the URL: http://online.sagepub.com/. You must register to have account and then you can try to acces the article. Use your key word to find those article. You can also use Google. But try get in to advance search and beside put in your key word use the file type. Choose the *.pdf or *doc, so you can find longer article than html file. You can also choose which years you want to begin your research. Good Luck on your research.