You can try Tutto Bene in Bsllston. We used their private room for about 12 people.

Del Ray PP here. I checked out some of the previous suggestions and here's what I found, to save you a little time:
Majestic and Liberty Tavern both do a very nice lunch but don't have a private space. Liberty Tavern recommended their sister restaurant Lyon Hall, but we didn't want Belgian, and there was a sort-of-steep minimum for the room.
Ray's the Steaks doesn't do lunch.
The private space in Boulevard Woodgrill is way too big for 10-15 people. It's in a basement and would be nice for a big festive occasion, but for this, it would feel empty and sad.
I initially thought McCormick & Schmick's, but we were scared off by some very poor Trip Advisor reviews.
Tallulah's has a really nice private space and great food, but it's a wine room and being surrounded by wine didn't feel right. (YMMV.)
If you have the wallet, there's a really nice sun porch room at Restaurant Eve. We didn't have the wallet for that.
The next closest thing that we almost did, which looked really nice, was Columbia Firehouse. It was a close call; Del Ray Cafe was lower key and more homey. It was really lovely.

I had this exact issue 6 months ago. We ended up in the upstairs room at Del Ray Cafe in Alexandria and it was perfect. A bit of a drive (10-15 min.) but totally worth it. They really took care of us.

Anonymous wrote:There's a McCormick & Scmicks in Crystal City.

This is what I was going to suggest as well.

There's a McCormick & Scmicks in Crystal City.

I would recommend Shirlington - maybe Carlyle?

We had a small event there for a group of 10. It was not a private rrom - but it was quite and nice.

Boulevard Woodgrill in Clarendon has a private function space.

Liberty Tavern in Clarendon.

Tallula's.

Thanks, PPs. The service is for my grandmother, who will be interred with grampa, a WWII vet. So we have a military connection (obviously) but no active duty presence to leverage for O club access. Is there anything in Crystal City or the Clarendon-Ballston corridor that might fit the bill? All I know at this point are the local burger and pizza joints. Sigh.

Are you or anyone else affiliated with the military, active duty, retired or maybe SES? Check with the Ft Myer Officers Club.

I'm sorry for your loss.

One of the hotels near by may have private dining rooms. Also did you ask the funeral director for recommendations?

I'm looking for a place where our family can gather for lunch following a service at Arlington. We'll be 10-15 people, including two kids (4&8). Would love a restaurant with a private room. Many thanks for any suggestions.