What's Our Part Again?

For harmonies, the teacher would go over our part one by one. He'd go over it once or twice and then expect us to know it at the snap of a finger. Harmonies can be difficult if you've never sang any before. They're especially difficult if it's a familiar song that you've sang a thousand times. Then the melody can sneak up as you're harmonizing and then suddenly you're asking, "What's our part again?"
I had a difficult time remembering some of our parts even as a senior in choir. What annoyed me most was that the teacher wouldn't realize that nobody in our section knew the part and there was only one person singing it. Maybe the reason sopranos seem so loud is because there's altos singing along with them.
We'd go over our part once and then three days later have a sectional. The problem was that there needed to be more than one sectional on certain songs but the teacher would only have that one. It made it really difficult for the people who were not used to harmonies to remember all of them. I have the feeling that if we'd just gone over them more often we would've been better as a section. That way the other sections would've stopped glaring at us whenever the whole choir was stopped so we could be told to sing louder.
Judgy eyes staring at us is really not helpful when learning. Especially since it's singing and many people are afraid of being judged for the singing. Usually we're a quiet group of singers and the thought of singing in front of other human beings is really scary. The fact that we didn't really know the part probably made us even less confident. Now we had to be afraid to be heard and afraid that we didn't know what we were doing.
I just wish that the teacher paid attention to these problems. A lot of problems would be solved if they took the time to fix them instead of pretending they don't exist.