Researchers investigated READY4K, a program in which parents received text messages over an 8-month period (York & Loeb, 2014). The goal of the text messages was to help parents prepare their preschool-aged children for reading. The children of parents who received the text messages were compared to a second group of children whose parents did not receive text messages. The researchers reported that the text messages led to “student learning gains in some areas of early literacy, ranging from appr oximately 0.21 to 0.34 standard deviations.” 

a. Based on your knowledge of mean and standard deviation, explain what this finding means. 

b. Did the researchers use a between-groups design or a within-groups design? Explain your answer.