What are your goals for the Head Start program and your DS3? (I'm leaving aside for the moment the help it's giving your DS2, since that isn't the goal for the program.)
I think your goals for DS3 are important to consider, because if the program isn't meeting your goals, and you want to keep using the program, then something ought to change.
Do you think the below-skill-level stuff the teacher is giving DS3 is harming him? Making him dislike the work? Dislike her? Feel like he knows everything there is to know already? If you said "yes" to any of these questions, then I'd say something needs to be done sooner rather than later. A talk with the teacher should be your first step, and you should talk to her soon! If that doesn't cut it, then you might need to advocate with the head of the program.
OTOH, if you said "no" to all of these questions and instead you just think the Head Start work is not as challenging as it could be, then it sounds to me like your DS3 is getting enough out of the program to make it worth continuing. Talk to the teacher if it feels comfortable to do, but don't make a big stink about it. You can always supplement the program on your own time with material that is challenging enough for your DS3...and let the Head Start stuff be more for DS2! Do what works!
