Rory wants to tests the effectiveness of a new reading curriculum with 2nd graders, and obtains permission for a study at a local elementary school. Rory measures reading ability for children (pretest), implements the curriculum over three months, then measures reading ability again (post test).

1) What are two methodological limitations of this pre-post design?

2) How can Rory improve internal validity by designing two group quasi-experimental study?

3) What changes must Rory undertake to conduct a true experiment to test the reading curriculum?