I've done church mission trips and I am not a fan.

For what was raised to cover travel (and a t-shirt) and taking care of housing and meals and supplies for the participants, that same money could be used to hire local labor to do the work (and likely faster and better than a bunch of teens) and put spendable money in the hands of the people who worked and done some good in the local economy.

On one trip it was planned to do a bunch of house painting. The paint was bought in Arkansas and the brushes and other supplies. $0 to local business in the place we "helped' likely negative dollars as some of that painting would have ended up being down without us and thus no sale of paint, brushes or supplies locally.