Some behaviorists, beginning with Charles Spearman, posit each person has a certain degree of intellectual ability called a g factor, or just g, standing for general intelligence or general mental ability. They observe that people who have higher achievement in one academic subject (such as language or math), tend to have higher achievement in multiple academic subjects, and people who have lower achievement in one academic subject, tend to have lower achievement in multiple academic subjects. Many believe the g factor accounts for this high correlation, that each person is born with a certain amount of g, and that this amount does not change throughout a person’s life. Even if this theory is true, attempts to measure a person's g as a single number have been less than perfect.

One common attempt to measure g is IQ, or Intelligence Quotient. Scientists design IQ tests to have a mean of 100 and a standard deviation of 15. About 95 percent of the population should score between 70 and 130 with scores above 130 indicating exceptional intellectual ability and scores below 70 indicating intellectual challenges.

As Christopher Shea reported in the October 29, 2012 issue of the Chronicle of Higher Education, James R. Flynn identifies a few problems with current IQ tests. For one thing, the tests indicate people are getting significantly smarter over time, which other measures do not confirm. Race and gender differences in IQ scores also exist. Some people believe the gaps in performance between black test takers and white test takers indicate differences in g, while others claim the tests themselves are biased.

Other people present alternate ideas, such as Howard Gardner's theory of Multiple Intelligences. The theory of Multiple Intelligences posits there are several ways for people to be smart. Children who excel at one of these intelligences often excel at others as well, but sometimes a child who is typically average is outstanding at one particular type of intelligence. This idea is appealing to many teachers, but, according to a Youtube video called “Theories of Intelligence” posted by Khan Academy, as yet has little or no data to support it.

You can view the video here:

Other Resources:

https://www.verywellmind.com/what-is-general-intelligence-2795210

https://en.wikipedia.org/wiki/G_factor_(psychometrics)

www.verywellmind.com/gardners-theory-of-multiple-intelligences-2795161

References:

Bartlett, T. (2011, December 21). Is intelligence in the genes? Chronicle of Higher Education

Carter, P. J. (2007). IQ and psychometric tests: Assess your personality, aptitude, and intelligence, 2nd edition.

Shea, C. (2012, October 29). IQ wars continue with battles over new puzzles. Chronicle of Higher Education.

Visser, Beth A., Ashton, Michael C., and Vernon, Philip A. (2006). “g” and the Measure of Multiple Intelligences: A Response to Gardner. Intelligence, 34(5) 507-510.