I am having difficulty which I bought the AE CS5 for home use meanwhile at my Campus the only offered AE CS4. Hence for the assignment I do in my PC which using CS5 but when I trying to access with AE CS4 in my campus workstation it appear error unable to open is because it create in version 10.00( unknown).
Yes, that is just the way it is. Project files of newer versions are not compatible with older versions.
As Mylenium said you can't sadly. Maybe you can try to install the CS5 trial version in your school so your teacher can check your work. That would only work for 30 days, and with limitations tho.