It depends on what their doing, if one is for Read/Write say Head Teach, and Recept and Teach are only needing it for viewing then Seperate EXE's would be ok, But if they all have diff level permission's as to what they can view and edit say Head Tech Full Access, Receptionist for Medium Level to log Appointments/ Students and Teach Meeting ect. and teachers low level for viewing and some slight Editing, then a single application would be better as Access to the Database would be from the main login and aloteasier to manage than seperate EXE's as all the forms on the single APP would beable to update each other alot faster also more manageable and not plastred allover the system, and as for security all the USER/PASS would be handled by the one app, i know this was long winded but before you decide to make a database front end you have to take in account what is needed and what you have to implement, Structure is important.
