A study published in Child Development found that students were 30 percent more likely to clean up when teachers said, "Can you be a helper in cleanup?" instead of "Can you help clean up?" [1]
A study published in Proceedings of the National Academy of Sciences found that people who received a letter encouraging them to be a voter rather than simply to vote were 15 percent more likely to register to vote. [2]
Extra: Emotionally Intelligent People add these 2 Letters to Certain Words to become Remarkably Persuasive - Jeff Haden
Extra: Motivating voter turnout by invoking the self