An update for anyone who might be curious:
The principal has not followed up with me since our meeting several weeks ago. I have no idea what may or may not have transpired with the science teachers at the school. I am disappointed that she did not follow up as she stated she would; however, I am not entirely surprised.
Good news: DS did indeed earn an A for all the work he put into that science unit. He feels proud of himself for what he accomplished and for doing well on it. That's a positive. He also learned a valuable lesson about why it's important to plan his work ahead of the deadlines.
The class has started the next science unit. In reviewing the schedule DS brought home, it appears that the kids have been allowed to do much of the work in class. I would have to say that some confusion continues because the kids were given a deadline of today to complete an assignment; however, the homework website says it's due Monday the 30th. I don't know how anyone is supposed to keep this straight. It appears that there are fewer assignments this time around.
DS told me today that some of the kids are still finishing work on the previous science unit. Evidently, the teacher has allowed them to continue work on the B and A layers even though the deadline passed. They have to do this on their own time. DS's opinion is that this is unfair because he put in all the extra time before the deadline, and these other kids will have the possibility of earning the same grade he did even though they're so behind. I can't say that I blame him for feeling that way about it. (Of course, I could speculate that perhaps the kids were allowed extra time as a result of my meeting with the principal, but I really have no idea.)
That's all I know. If I ever hear from the principal, I will post an update. Thanks again to everyone for their ideas and suggestions!