They aren't really duplicates in the database sense
Some idiot gave them separate class codes on the school's main Sims database (which I have no control over)
The Sims database runs a report daily to update my database with Firstname, Lastname, UPN (a special unique number to each student), Maths group and the empty column mathsteacher
this is stored as a CSV file at about 3am and I update my tblStudent on my access DB with it daily.
So one of John Smiths classes is a Maths class. The shorter one!!
I eventually cracked it with this thanks to Aytee111's advice and link
Code:
SELECT tblStudent.*
FROM tblStudent
WHERE (((Len([tblStudent].[MathsClass]))<>(SELECT min(Len(Mathsclass)) AS Mathsgp FROM tblStudent AS Dupe
WHERE (Dupe.Surname = tblStudent.Surname)
AND (Dupe.FirstName = tblStudent.FirstName))));
Thanks