Acknowledgements: Thanks to Roger Sprik on the PowerSchool forums for this tip.
I have a custom page that uses the last name field:
~([05]Last_Name)
The only problem with that is if the last name has an apostrophe in it, that can lead to unexpected stuff when used in jQuery.
Apparently, you can strip out the variable to show only the letters and numbers:
~([05]Last_Name;keep_ascii=48-57,65-90,97-122)