You have to set it up beforehand, and it's tricky to do without exposing yourself to security risks.
There are several options :
1. use a connectivity tool, such as PC anywhere or GOTOMYPC to remotely connect to the other PC.
2. Set up a publicly accessible folder on your PC & connect to it from school (you will need to know the ip address, which typically changes from time to time, unless you paid for a static address). You need to turn file sharing on for this, which is a security threat.
3. an easy work-around, if you use internet based email, such as Yahoo, would be to keep the most current version of the document in a draft email - then you can access it from anywhere (but again, you have to plan ahead for this)
4. Why not use a USB thumb drive & carry it with you - that way you always have the most recent version.