QUESTION $21$

Dr$.$ Kenji wants to determine whether his new ph$$nics program helps children's reading comprehension. He gives a fith grade class the program and also studies a second grade class that does not go through the program. He finds that the fifth graders read with better comprehension. Identify the confounding variable in this research design.

the phonics program

the grade the students are in

reading comprehension scores

not giving one group the program