You do have SQL Select statements in FMP 13. Take a look at the ExecuteSQL function (NOT the script step). And if you can use that function to return an ID or a list of ID's, you can then use that list in a relationship to pull up the full record or group of records.
Is the only difference between a pre and post test, the date on which the test was taken?
Have you imported the dates into date fields? (not text fields)
You can easily use a relationship or a find to pull up all records with a given Student ID. These can be sorted by date so that the first record would (presumably) be the pre test and the second record would be the post test.