A system and method for performing DSL assessments of a telephone line along a prescribed test path is disclosed. The disclosed system includes a loop diagnostic test unit adapted for testing said telephone line using narrow-band and mid-band frequency test signals; a test system controller and a test system server to provide the DSL assessments to a user via an appropriate interface. In addition, the disclosed methods include the basic steps of: accessing the telephone line along the test path that includes selected hardware such as a voice switch test bus, central office splitter, service provider instruments and terminations; ascertaining various line characteristics along the test path using mid-band and narrow-band frequency signals; analyzing the line characteristics to identify line conditions that affect DSL service; and determining the impact of the line conditions on DSL service.