The third variable which may cause this correlation is the IQ score.
What is IQ score?
This is referred to as intelligence quotient and is a type of standard score that indicates how far above, or how far below an individual stands in mental ability of his/her peer group.
IQ score will be the most likely third variable as it brings about a correlation between a student reading and score gotten. This is because with a higher IQ score are more likely to get higher grades and vice versa.
Read more about IQ score here https://brainly.com/question/25808480
