I don't think this meets the "textbook" definition of a "join" table as it appears that you want one record for each unique student in your "join" table. You can omit duplicates as part of the import records process.
For that studentname field, you can specify field validation options of "unique values" and "validate always". Then you can import data from either or both excel files into this table and names will only be imported once. Subsequent duplicates will be omitted automatically--producing a table of just one record per student name.
But you'll need to look out for the possibility that you might get two students with the same exact name. (And student names can change on you too--such as when a child undergoes a step parent adoption and takes the last name of the adopting step parent.)
Thank you for the reply. As for the "Unique Values" validation, would two students with the same name but in different classes be seen as Unique, or does it only work on one field?
For example is John Smith in Class 1 seen as a different person to John Smith in class 2?