Debate is ongoing over how much of a person's intelligence comes from genes passed down to them from their parents, but estimates put hereditary on a par with the environment a person is raised in. This is the "nature versus nurture" debate. Still, it is clear that heredity plays a strong role in determining a person's intelligence. Studies of identical twins--whose genomes are essentially the same--show that they will score similarly on standardized tests even if raised in different homes.
While genetics provide a person with the capacity to learn, general good health and a stimulating environment are also necessary to build a person's intelligence. In addition, a solid education provides factual knowledge, increases vocabulary and provides the opportunity to practice analytical and computation skills. Studies of identical twins show that their IQ scores will be even closer if they are raised in the same household, with the same parents, health care and education.
The ability to take a test well is a learned skill. Test-taking skills such as reading all directions carefully, budgeting your time, managing anxiety and using memory-jogging techniques have all been shown to increase IQ test scores. Also, practice answering the types of questions that are on an IQ test may increase your score.
One person can take the same test on different days and have different results. Eating well and getting enough rest before an IQ test are known to increase scores.
IQ tests have been criticized for having a bias against some segments of the population. Also, IQ tests primarily measure linguistic, mathematical and logical intelligence, but do not measure other types of intelligence, such as musical, spatial and interpersonal.