I am on T10 ADOS orders for my unit. Am I required to attend BA while on these orders? Or is it at the discretion of the commander?

It depends on organizational politics and where your orders has your place of duty and how long you are tour. If it is "for your unit" the prudent soldier would be at BA because you are on duty 24/7 for the period of the orders. If it is for duty at a higher HQ and travel back is impractical, then negotiate/explain your situation with your chain of command. Keep in mind, you will not be paid twice for that duty (just saying) but if you keep everyone happy you might be permitted to "make up" your drill dates. As an old unit administrator, when I had a troop go "on short tours" I would talk to them that the tour was a privilege at the convenience of the command and how if they wanted to do more tours they need to keep the relationships "healthy" and mutually supportive....ie, do not burn any bridges.

There are two common scenarios here which could match your question. One resolves to 100% yes, the other to a practical 90% yes.

First (the question as you actually stated it), you are on ADOS order FOR your drilling unit, i.e. Your full-time job is currently at the same unit you drill with. It is the same CoC that you were under before. If so, you should think of yourself EXACTLY the same as the AGRs & mil techs there. (In theory, they show for drill....) Confirm with the command, but I would expect to attend all drills.

Second, you are on ADOS orders somewhere OTHER than your drilling unit. In this case, it can be .... tricky. The BOOK answer is that while mobilized you belong to the unit that you are attached to, not your parent unit. TECHNICALLY the parent unit cannot MAKE you drill. However, if they (your parent unit) wants you to drill and your attached unit does not forbid it, I would do everything in my power to attend. See LTC Thomas Tennant's comments. About the only time I would NOT advocate drilling would be if it would require air travel to get there & back. Even then I would strongly consider it.

What should happen: Your unit should code you either S (RST) or B (on orders) for those battle assemblies. Most likely B if its for a year or more, as the RST window is normally 60 days plus or minus the battle assembly being made up. You're on orders..which is not a privilege, it's active duty for the benefit of the Army Reserve and the Army as a whole.

What will happen: If they want you at Battle Assembly, and you don't show up, they'll likely get your ADOS orders revoked.

Ask the question of your unit, and follow the instructions given. It is what it is.

I know this thread is old but I just ran across it so I figure others may need it in the future.

AR 135-200 Chapter 6-2d:
"Soldiers performing ADOS will not attend IDT or AT with their unit of assignment"

AR 135-200 Chapter 6-27e:
"Soldiers are not authorized to participate in battle assembly or AT with the parent unit while performing ADOS–RC duty with another unit or headquarters. However, Soldiers are required to provide administrative information, such as a DA Form 705 (Army Physical Fitness Test Scorecard) and DD Form 2795 (Pre-Deployment Health Assessment), to the parent unit upon request.

Where does this state that they 100% have to attend if they are on ADOS with their parent unit or a different unit?
It does state in Ch6-2c "ADOS will not be used for training, to include attendance at professional military education or other training and development courses." And last time I checked Inactive Duty Training was considered training.

Everything that I have read stresses heavily on the "not authorized" part and I haven't seen anything that says "at commanders discretion" or "you scratch my back and I'll scratch yours".

you attend BAs

Totally digging your Brotherhood of Steel pic