Congress' conservative members speak, on average, at the lowest grade level. Moderates from both parties tend to speak at the highest level. But collectively, the legislative body speaks at a higher level than the average American, who reads at between an 8th and 9th grade level.
Here's a little context: most major newspapers clock in at between an 11th and 14th grade level. The Gettysburg Address was at a 11.2 grade level. Martin Luther King Jr.'s "I Have a Dream" speech was at a 9.4 grade level. And President Obama's State of the Union addresses come in at around an 8th grade level, according to the study.
Rep. Dan Lungren (R-CA) grabs the top speaking level at 16.01. Rep. John Mulvaney (R-SC) bring up the rear at 7.95. It would seem silly to suggest that a politician's speaking level is an indicator of his or her legislative success. Especially when the study concludes that the more words individual members speak on the floors of Congress, the simpler their speech tends to be. The grade levels were calculated using the Flesh-Kincaid readability tests, which equates longer words and sentences with higher speaking levels. The Sunlight Foundation is a non-profit, non-partisan organization interested in increased government transparency.
Here's an info-graphic from the Sunlight Foundation charting the findings (click to enlarge):