Good days to all.

I have created a grade summary spreadsheet using Office 365's version of Excel.

I have a total of 4 teachers who have access to this spreadsheet to enter grades and other reportable data onto the spreadsheet. There are 33 students.

There are two problems with the security of the worksheets:
1) Worksheets seem to be moved from time to time. The sheets are set up alphabetically, yet occasionally sheets will be out of alphabetical order.
2) Data in cells is either missing or corrupted.

Is there a problem with the application? Is it a misapplication of the Xcel program to have one workbook being edited by 4 teachers?

Any ideas would be appreciated.

You can use some VB code to order the sheets found here.

Just run the macro, and all the sheets will be sorted automatically.

As far as the corrupted data goes, it could be an issue with the autosave function. If the spreadsheet is being accessed over a network the autosave may misrepresent the data when office tries to reintegrate or there are simultaneous threads opened.
Try turning autosave for the document, instructions here.

Alternatively you could lock cells once data is entered to preserve them from being edited.

You may also be having an issue with multiple instances being opened at once, do you find that there is a second copy of the file being created somewhere?