Research has indicated that seventh- and eighth-graders who outscored most high school seniors on a college aptitude test had begun at an unusually early age.

The correct answer is reading.

Several research studies over time have found that early reading leads to higher intelligence in children when they are older. Early reading leads to better vocabulary skills, general knowledge, abstract and reasoning skills, concentration skills and comprehension. This is why early readers perform well on IQ tests and aptitude tests. 

Hey here is your answer