First, I would like to start out with the disclaimer: I AM NOT A TURF EXPERT, however, I have been asked to help with a few turf problems. Many think they can just throw out some grass seed in their yard, and a lush, green, lawn will grow. But sometimes, it's not that easy.
The very first question that I asked was if this site consisted of alot of clay, and their answer was, "Yes, there could be some clay there." The next question that I asked was if they had a soil test. Their answer was, "We just took soil samples." I said that I did not want to go any further without seeing their soil test results. It was too bad that they did not soil sample 2 years previously, when this grass was first planted, because I just found out that the soil tests revealed that they had soils with a pH of 8! Turf grows best at a pH of 6 - 7. They will now need to add sulfur to try to raise the pH.
Here is a good website to help with site preparation in lawns-
Here is a list of soil testing labs in Illinois-
Here is a website that explains other problems in turf-
Here a factsheet on spring lawn care-
I really like this "oldie, but goodie" article by Sandy Mason-(fall is an ideal time to seed a lawn)