Insect and Spider Identification: Please help ID tiny black specks, 1 by UrbanBonsai

UrbanBonsai wrote:
Please help! TINY black specks on underside of leaves on my Chinese elms and Hawthorn. This has been a reoccurring pest for at least 4 years now. It's on the underside of all the leaves on each affected tree, and I mean ALL the leaves - the ENTIRE tree. The spots don't seem to damage the leaves or tree; growth has always been healthy so I haven't worried too much, but a couple of my trees should be ready to show in a year or two and I'll definitely have to rid myself of this before then.
The specks don't scrape off easily by fingernail, at least without damaging the leave. I've tried neem oil to suffocate them, and I experimented with brushing diatomaceous earth on them with a q-tip, but neither had any effect. When I do scrape one off, it's thinner than paper and doesn't seem to be an insect body... but it's too small to say for sure. I searched online for different species of scale and that doesn't seem to match. I need ID to research life cycle and find out how to get rid of them!