In the input query, use sub-query which is itself a MIN query by student ID.
Add the min value to the reports query. In the OnDisplay event, check the
MIN value against the rows displayed value, if the values equal, change the
format values (bold, italic, etc.). If you want to designate with an
asterisk, create a constant value text box (control source value of ="*") and
use its visible property when the min equals the current.
With this method, you can determine multiple scores which are all the same
MIN value.
This method can be expanded to show the minimum score per test and expand
that number to each student. This would entail using the MIN sub-query
against each test date, across all students, and add the MIN value to the
reports query.