Dave, I have good news for you. It’s entirely possible that your IQ is average or above average. Though IQ is our best measure of cognitive ability, it is a rough approximation, especially for children at an early age. During your early formative years, your brain was producing and pruning neurons at a prodigious rate, forming connections between neurons, called “synapses” and building your intelligence. An IQ test is a snapshot of your cognitive skills at a particular point in time, and the result of an IQ test taken at age 5 should not be taken too seriously. A 5-year-old is often distracted while taking the test, or is having trouble understanding what is being asked or what he or she is expected to do. Furthermore, the IQ is based on the average performance of students at a particular age, but brain maturation does not follow the same timeline in all people. We all mature at different rates.
Recent research indicates that while the average IQ of those in the same age cohort is relatively stable over a span of several years, the IQ of an individual can change significantly during this period. In a longitudinal study, 33 teenagers of average age 14.1 years were administered an IQ test and a structural brain scan in 2004 and then again in 2007, when their average age was 17.7 years. It was found that during this period, the average IQ of the group had changed very little; however about 20% of the participants showed a positive or negative change in IQ of at least 15 points (one standard deviation). Furthermore, magnetic resonance imaging (MRI) revealed that positive changes in IQ corresponded to increased gray matter in sections of the brain associated with those cognitive functions. Summarizing their findings, the researchers, Sue Ramsden et al. (See Nature. Vol. 479. pp. 113–116) reported:
Our results emphasize the possibility that an individual’s intellectual capacity relative to their peers can decrease or increase in the teenage years. This would be encouraging to those whose intellectual potential may improve, and would be a warning that early achievers may not maintain their potential.
Indeed, you may well have above average IQ. I would recommend that you stay intellectually active, challenge yourself with puzzles and mathematical problems, and continue to believe that you have a strong intellect. That will stack the odds in your favor.