PHP filter list from other list's selection

I want to filter one list from the selection of the first list. The second list will use a recordset to find the records to display that match an integer field with the number value of the first list.

This seems like it should simply work by using a simple mode of the recordset that compares the value of the the field in this recordset with the Form Variable that equals "lstLevel", the name of the first list. The form action = the current page. Then I have a submit button on the form, but when I press it nothing happens. What am I missing?