To test the effect of day care on academic performance in young children, a researcher plans to use two groups of 5-year-olds from the same kindergarten class: One group is made up of randomly selected children who attended day care, and the other group includes randomly selected children who did not attend any day care prior to attending kindergarten. Both groups will complete a brief test of academic performance during a class. Which type of test should the researcher use to compare the mean scores of the two groups