​Dr. Swartzman wants to know if children who are raised in l…

​Dr. Swartzman wants to know if children who are raised in lower socioeconomic environments have more difficulty succeeding in school as they grow up. He enlists a group of four-year-old children and their parents, and he observes the children in school twice a year until they turn 18. Dr. Swartzman’s study would be best described as