Unlike certain medical tests that have a standard time frame to repeat, there is no set schedule of when IQ, academic achievement, neuropsychological, or psychological testing should be done. Once a test battery is completed, the benefit of re-administering the tests at a later date is to measure progress.
Most psychologists would say that at least one year should pass before testing is repeated. This may even be too soon as progress with learning disorders and Asperger’s Disorder is slow, and measurable success may not show up after one year. Two to three years is a more reasonable time frame that allows the child to benefit from the academic, behavioral, and psychological interventions. There can be exceptions to this general recommendation.
If testing is to be done more frequently, there should be a specific purpose and a plan for modifying interventions based upon the results. Retesting should involve a comparison of both sets of test data. Having the same psychologist administer the retesting has the advantage of his experience with and prior knowledge of the child. If you choose a different psychologist for a retest, be sure they are provided with the previous test data and written report so they may do an accurate comparison.