Singular They, Them

[10x]

There are several different ways of writing the following. Which makes more sense to you? 

Ignore the fact that you could replace teacher with a name because this same model will be used many times in a 200-page book. This applies to a bunch of scenarios such as a spouse, a patient, a lifeguard, etc. where the gender isn't known or even very important. 

Note that this isn't about gender equality or anything like that. I'm just trying to figure out the best way to get my point across. #1 and #2 seem stuffy to me but while #3 is more and more accepted, there are a lot of people who would say it is wrong and judge the author negatively. 

1. The teacher was told s/he needed to get his/her things together and leave the premises by 2:00 PM.

2. The teacher was told she or he needed to get his or her things together and leave the premises by 2:00 PM.

3. The teacher was told they needed to get their things together and leave the premises by 2:00 PM.

Thanks.