A Google Web Search product manager announced a new Google search filter for reading level on the Google Web Search Help Forum.
"Sometimes you may want to limit your search results to a specific reading level," the company explains. "For instance, a junior high school teacher looking for content for her students or a second-language learner might want web pages written at a basic reading level. A scientist searching for the latest findings from the experts may want to limit results to those at advanced reading levels."
The filter can be accessed under Google's "advanced search" link below the search box. If you go to "Reading Level" you will get options for "no reading level displayed," "annotate results with reading levels," "show only basic results," "show only intermediate results," and "show only advanced results."
Barry Schwartz, who happened upon this announcement, had the good idea to perform a site search to what percentages of your content Google has deemed basic, advanced, and intermediate. This could provide a good guideline for addressing how well your content is written for your target audience. For example, are you trying to be an expert that other experts and those aspiring to be experts turn to or are you trying to keep things basic?
I don't know how often users break out Google's advanced search options, especially now that there are so many options on the left panel, but the feature could definitely be useful in research, and for educational purposes as Google described.