I understand your point, but there are many HS students who have research experience. IME, it’s not rare. For example, my D did research as a HSer in a lab at a local T20 uni, and there were three other HSers in just her lab. There were many other HSers on that campus participating in research too. Just my two cents from someone who works with HSers in the college admission process.
With that said it is a great EC to have, and as I said above I do think you S should include it on his resume and common app activities.