Pondering a math problem while she swings her sneakered feet from a chair, 12-year-old Andrea Guevara is helping researchers design an assessment that will shape the learning of 19 million students. The 8th grader, who came to the United States from Ecuador three years ago, is trying out two ways of providing English-language support on a computer-based test. Three researchers watch Andrea closely. Andrea has been encouraged to think aloud while she's solving the problems, researchers hear as well as see how the features of the different test items help or hinder her. Held at a middle school here last week, the session spotlighted an important but little-known piece of the test-making process, known as cognitive labs. With their intimate scale and their dive into a student's experience with the test, cognitive labs allow scientists to get inside students' heads and use what they learn to craft easy-to-use questions and tasks.