A practical example of a pretest-posttest nonequivalent groups design involves assessing an anti-drug program across different schools. Students in one school take a pretest on their attitudes toward drugs, complete the program (treatment), and then take a posttest. Students in a similar school take the same pretests and posttests but do not receive the program (nonequivalent control group). By comparing the pretest-to-posttest attitude changes between the two schools, researchers can determine if the treatment group changed significantly more than the control group, helping to rule out general confounding variables like widespread historical events or maturation.