Other than a person's intellectual ability, there are a few other factors that play a part in determining how he performs in an IQ test. Following are some of the most influential factors:
Genetics. Studies have shown that IQ is partly inherited from one's parents. In other words, there is a good chance that someone's IQ will be approximately equal to the average of both his parents' IQ scores. Of course, this is not always the case but it is true for majority of the population.
Education. Although IQ tests are meant to measure intelligence that has nothing to do with academics, there is no denying that people who have received good education are more likely to do better in the test than those who have not been educated at all. This is not necessarily because of the lessons that are taught in school but more likely because of the mental training that he has undergone as a result of these lessons.
Environment. This includes the physical environment at home, in school and in the workplace. For example, cluttered surroundings often make for a cluttered mind, and so people who are rather messy with their things tend to score lower in an IQ test than those who live in a clutter-free environment.
Favorite Activities. IQ can increase or decrease over time, depending on how the brain is used. A person who likes to read or do Sudoku puzzles during his free time, for instance, is likely to have a higher IQ score. On the other hand, a person who just likes to spend the weekend on the couch flipping through the television channels might suffer an IQ decrease over time.
These are just some of the factors that can affect how a person performs on an IQ test. Other possible factors include his mood at the time of taking the test, his emotional health and his level of stress.