Let guest account use Boot Camp
You can use the following code to create an Applescript application to accomplish this.


  do shell script "bless -mount \"/Volumes/Boot Camp Name\"
  -setBoot -nextonly" user name "admin username" password "admin password" with administrator privileges
  
  do shell script "shutdown -r now" user name "admin username" password
  "admin password" with administrator privileges


You will need to:


Paste the above code into AppleScript Editor
Fill in your admin username, password and name of your bootcamp volume where necessary


Once your details are entered you can save the script for editing later and then export it (File > Export) as an Application, making sure to check the "Run-Only" box before clicking Save.  What this does is create an AppleScript application that can only be run, not edited or viewed.  When you launch the application your Mac will temporarily reboot into whichever volume you specified in the code.

The following accomplishes this:


bless &amp; setboot - This designates the default startup disk
nextonly - This tells the system that the volume designated in this command should only be the startup disk for the following boot, subsequent restarts will boot to the proper startup disk.
shutdown -r now - This tells the system to reboot now 
Exporting as a run-only AppleScript application allows the students to execute the command but not view the contents, which should keep the admin credentials safe.  I made a sample application on my system and was unable to view the script inside the application by digging through the package contents.  It may be possible to get around this but I couldn't find a direct way.


To make this accessible to Guest users in addition to standard user accounts you could add it into the default user template at /System/Library/User\ Template/English.lproj/.  Settings, files, etc in this location carry over to the "on the fly" Guest accounts available in the newer Mac OS X revisions.

Hopefully that does the trick for you!