Next summer I plan on chaperoning two teenage daughters who will be studying Spanish and living with a family while I "lurk" in case an emergency occurs. I am interested in any recommended day trips I can take by bus from Sevilla. Any thoughts? Thanks in advance. Mike

There's so much to see in Sevilla you'd hardly need to take many day trips. But here are some obvious ones. (getting progresively further away, but all are feasible in a day)
1. Very near town, the Roman ruins of Italica
2. Cordoba
3. Ronda
4. Jerez
5. Cadiz
6. Granada

Barry's suggestions are all good ones. I'm not sure if you want to do Granada in a day trip, though. Maybe if the girls are settled in you could get away for an overnight trip. Sevilla in the summer can be very hot. Getting to the beach is always a good bet. Some of the best ones are south of Cadiz. Aracena is a very pretty mountain town with a really cool cave, if you want to escape the heat. It is also in the area where they make some of the best jamon and chorizo iberico. Don't miss it.

Another thought, as long as you are hanging around with time to kill, if you want to learn or improve your Spanish, go to language school and travel on the weekends. I spent 13 weeks in language school in Sevilla and loved it. (And yes, I am over 40!) You've got a great idea. I can't wait until my kids are old enough to send over there and I can "lurk" a while, too!