The conversations go like:
Me: What are you here to do?
Them: Build a school.
Me: Oh, you are a carpenter.
Them: No, part of a school program.
Me: Oh, you are providing unskilled construction labor. Didn't realize Tanzania had a shortage.
Near the end of the trip, I met a friend's cousin, asked what she was doing, and she was going from village to village verifying that chlorination systems in NGO built wells were working. I was impressed. I asked how she got that gig, and she told me a story about her going to Tanzania to build a school. She decided to make a real difference.
Her story changed my attitude. I am certainly less snarky about kids going to do unskilled construction labor.