Welcome Nicky! I'm just jumping in to add my 2p-worth (I'm in the UK so my thoughts are valued in p not c) as another non-tester. By the time we thought about it, it was clear - as I think it is to you - that we'd expect DS to test in the region where the tests aren't really that meaningful, and that if he didn't we'd suspect the test rather than our judgement, at least on days when we were being rational. So it seemed pointless. DS's school raised the issue once. We asked them whether they felt test results would be useful to them in working out how to teach him. Not really, they said, given that they knew him well by that point. It seemed that they expected - maybe based on other parents? - that we'd want the data, but had no need of it themselves.
Many people, of course, do need scores for advocacy purposes, and some find them helpful for themselves, especially if they find themselves prone to second-guessing and/or there are inconsistencies in how the child presents that suggest some special support may be needed.
A middle road position might be to find out all about testers in your area who have experience with HG+ children, e.g. know their reputations, costs, likely waiting time to get a slot, and mentally make a plan and put aside the money in case you need test results... but don't actually put the plan into operation. You may find your school is great and really looks at your child, and you have no need of numbers.
