Tom Rogers wanted to test a new "singalong" method to teach math to fourth graders (e. g., "I love to multiply" to the tune of "God Bless America"). He used the singalong method in his first period class. His sixth period students continued solving math problems with the old method. At the end of the term, Mr. Rogers found that the first period class scored significantly lower than the sixth period class on a mathematics achievement test. He concluded that the singalong method was a total failure.

1. Identify the independent variable(s).
2. Identify the dependent variable(s).
3. Identify any confounding variable(s).
4. Propose a method to "unconfound" the experiment.