@Auntbea-
I would be very comfortable sending my kids to Oaxaca. In fact I have. My kids are Caucasian and speak imperfect Spanish, but they have all travelled without parents as teens to stay for an extended time with their grandmother in Huatulco (on the coast in the state of Oaxaca.) They’ve also gone into the mountains to help with school projects in some of the more remote villages. As a family we’ve spent time in the city of Oaxaca on multiple occasions. It’s a beautiful, historic city and I would highly recommend it.
There were teacher/union riots in 2006 and at that point I would not have recommended sending a child to the city, but those issues have been settled for years. As with any place, it’s smart to be aware of one’s surroundings, but I have never felt unsafe in Oaxaca. As for general safety warning about Mexico, it’s important to take them with a grain of salt. There are parts of Mexico I would not visit myself, much less send a kid to, but then I would not send my kids alone to parts of the US.
The perspective of the Lonely Planet Guides’ editor:
http://www.huffingtonpost.com/lonely-planet/are-tourists-safe-in-mexico_b_1503288.html
an excerpt-
http://howsafeismexico.com/mexico_states_safety.html
Here’s an expat site for the Oaxaca region. It’s a great place to ask Americans who live in Mexico for advice.
http://tomzap.com/ph5/index.php
I hope this is helpful!