I went through the knowledge test prep program three times.  The first time was before I started flight training, second was during the start of my flight training and then the last time was a week before I took the test (and after 40 hours of flight time).  I felt it helped me prepare for the knowledge test.  I didn't take any other type of ground school.  I got an 88%.  I would have done better, but I had injured my back a few days before the test and I was in discomfort during the test and just wanted to finish.  Otherwise, I feel I would have easily gotten in the mid-90's.
                            
                            
                                
                                    Thomas L.
                                
                                
                                    01/27/2015
                                
                                Private Pilot Online Ground School & Test Prep