Auto Populate Distinct List From One To Another Table

I have two tables on two different worksheets. I would like to automatically populate a distinct list into column A in table 2 from the data in column A in table 1.

Table 2 must auto populate from table 2 every time a new row is added into table 1 - without any extra user interaction e.g. pressing a button etc. No offense intended to my better half but if she has to do anything more than enter a new row in table 1 she'll likely manage to screw it up after a week

I kind of managed to get it working using the below formula but both sets of data must be in tables so I can't copy the formula down the column without creating redundant table rows.

=INDEX(Classes!$A$2:$A$999, MATCH(0, COUNTIF($A$1:A1, Classes!$A$2:$A$9), 0))

Example

Sheet 1 = "Classes"
Column A = "Student Names"

John
Mike
Paul
Andrew
Paul
Paul
Mike

Sheet 2 = "Total Due"
Column A = "Student Names"

Paul
Mike