OP here. Thanks for the suggestions!

Try contacting UpCycle in Del Ray. The ladies there are former teachers and they are great with kids when we have attended their open tinker sessions. They may be willing to do lessons or have suggestions for you.

Create arts center in silver spring

If it's not too far, Glen Echo has classes in crafts, textiles, paper for kids:
http://www.glenechopark.org/sites/default/files/Catalog_FW16_finalweb.pdf

What about something at the Torpedo Factory? I would see if you could do a drop in class to get a sense of what the teacher is like.

One of my low tone kids really likes working with clay; the other really likes painting at an easel (abstract of course).

There are other abstract forms like collages, photography where fine motor skills are less of an issue (like in drawing.)

My DS (ADHD/LDs/anxiety/tone&fine motor deficits) is in the 4th grade. He's always liked to draw and paint. He has volunteered that he'd like to take art lessons. This is a kid who has NEVER expressed interest in or liked any of the extracurriculars we signed him up for. We're over the moon! But! I'm concerned a typical Saturday art class might not be a good fit for him. He needs a patient and encouraging instructor. Anyone have any recommendations for instructors or classes? We're in the Springfield/Alexandria area. Thanks!