Renovate or establish a lawn in late summer
The cooler temperatures, adequate moisture and less weed competition make the middle of August through September most favorable to sprout seeds and grow grass seedlings.
You need to know what you have. You can determine if you have high clay or sandy soil by feel (video below). Simply squeeze a moisten soil sample in your hand by rolling your thumb across a clump of soil on your fingers. If the clump feels gritty and falls apart it is sandy. If you can form a sticky ribbon that is longer than 2 inches it is a clay soil.
Soil testing will provides a good measure of the availability of phosphorus (P) and potassium (K) and the pH level. Allow 1 to 2 weeks for soil test results to be return from the testing lab.