A Researcher Tested a Group of Students First Time in Second

Multiple Choice

A researcher tested a group of students first time in second grade and the second time in the middle of the third grade. The second test indicated significant improvement, but after reviewing the test scores the researcher became concerned that he could not be sure whether the scores were a result of the treatment or a result of the students' having gained more life experience in a year-and-a-half. What threat to internal validity is this researcher worried about?

A) Maturation
B) Testing
C) Differential selection
D) Instrumentation