Mr. Gregg wants to help his second-grade students improve their reading skills. He tests the students with 20 reading comprehension questions at the beginning of the
year. Every week throughout the year he gives the students 30 minutes of reading
comprehension tips. He tests the students at the end of the year with 20 reading
comprehension questions that are similar in difficulty to those in the original test. He
finds that the students' reading comprehension has increased and concludes that his
tips worked. Which of the following describes the most significant problem with Mr.
Gregg's study?
A.)Mr. Gregg failed to account for changes in the students' maturity
B.)It was unethical of Mr. Gregg to test the children without their parent's consent
C.)Mr. Gregg should have used the same test to ensure reliability
D.)Mr. Gregg should have had someone else test the children in case he was showing
experimenter bias
E.)Mr. Gregg should have tested his students every month so he could more accurately track their
progress. The answer is A but i need an explanation as to why it’s correct and why the others are incorrect