Pedal power is in Severna park so a bit of a trek, but they have private lessons and I bet he wouldn't need many to feel comfortable.

Valley Mill camp has a good kayaking program. It's a regular outdoorsy type camp, but that's part of the day. And instructional swim.

REI has both Learn to Kayak and Learn to Bike Classes: https://www.rei.com/events/search?previousLocation=gaithersburg+md&course.session.anyLocation=100.000000~39.143969~-77.201606;geo_r

You could do a kayaking class together. It really isn't that difficult to learn the basics! Not sure if I kid could do the REI classes solo.

Rock Creek Elementary school used to host a free learn to bike clinic one weekend every fall. Not sure if they still do it. Most kids left after an hour or two with the basics down.

Basketball I think your best bet is just to look for a rec league (Rockville has a good one with kids of all abilities). If your child really isn't interested though that might be a hard sell. It's also okay though if he never learns. It is a nice skill to have if he's ever in a situation where pick up games are a thing, but if it's truly not something he enjoys or is ever likely to enjoy, he won't totally be missing out.

Calleva has a kayaking summer camp (though he may be too young to enroll in the one that is just kayaking, but they have a water sampler camp that will include kayaking). During the year, I believe (but am not positive) they also have lessons but I’m not sure of the age requirement or how those might work.

Immigrant troll says don’t kayak in winter

My unathletic son learns how to swim after taking 3 years of swimming classes at age 8. I am comfortable for him to go to pool not dying, and he is still taking swimming classes with private instructor & group classes to learn to swim. Now, it comes down to basketball, biking and kayaking. I can't bike, can't play basketball or kayaking.

We live in Gaithersburg. Any recommendation for basketball, biking or kayaking classes? He is about to be age 9, thank you.

He is interested in kayaking, and it is getting colder. If there are any recommendation of kayaking summer camp, I will take it as well.
For basketball, he is not good at eye body coordination. It is ironic that DH knows how to play basketball, and he plays basketball for 10 plus years. Our son does not want to learn from DH. For biking, he tries for years but he is not good with balancing. DH does not like to teach him biking.