append only recrds which have been previously appended (1 Viewer)

[Happy YN]

I have an append query to append pupils id from a specific class into another table for each test that they take in various different subjects. however only part of the class take this particular test. Rather than append the whole class I would like to set criteria where it will only append those that are already appended in the big table for this subject because they have taken another test previously in this subject. How do I go about specifying these criteria in the sql statement? I do not want to create a seperate class with these pupils because they are all in one class but different groups of them take different tests in different subjects

Also supposing someone drops out of the group or enters this group how can I give the user control to update these details?
Thanks