I'll add:
You touch on something that is a big part of why we haven't tested our DS: the dark side of the idea that an IQ test may give valuable information that adds to what everyone sees by looking at the child is that an IQ test may give misleading information that subtracts from what everyone sees by looking at the child (including by influencing what you think and how you behave in an way that is irrational). I think this is a reasonable worry, particularly as you don't seem to have a question, as such, that increases the expected benefit of testing, so the risks loom larger.
You ask, how accurate are IQ tests. As psychological tests go, remarkably, in the sense that the correlation between a person's scores when tested on two different occasions is high, as these things go - but it turns out that's not saying all that much; big test-retest differences happen at a frequency that feels like "often" to someone more used to physical sciences. More importantly, IQ scores (even if you have all of them, and even more so if you only look at the headline number) are a crude abstraction of children's needs and abilities. FSIQ may be about as good as any abstraction that takes in a child and gives out an integer could be, but that's what it is! Many other things are important to success, both in education and in life.
Explicitly:
- Risk that you test your DS, he scores lower than you expect, and you react by deprioritising thinking about whether he needs more challenge and advocacy
- Risk that you test your DS, he scores higher than you expect, and you react by raising your expectations of him in an unhealthy way (like what was done to you).
These apply both to testing privately and to letting the school test, but more strongly I think to the former, because:
Advantage of not testing privately but just letting the school do it: you will find it easier to disregard the results and do the right thing anyway if they aren't reflective of what you see, than you will if the non-reflective results come from testing you chose and paid heavily for.
Suggested exercise: browse some of the IQ test threads here, and then *write down* a guess as to what your DS would score on each of the main indices. Imagine you have tested him and he actually scores that. How do you react? Is that the right thing to do anyway? Why, or why not? Suppose the numbers were different - what difference would it make, and why?
