We’ve been in August the past 2 years and are going again this August, because of school schedules too. It’s crowded but not to the point that you can’t enjoy the trip. It is hot and very humid, plan for afternoon showers. We always go to the parks in the morning and come back and swim a little then go back out for the evenings.
The only park that seems to be really crowed and can be unpleasant is HS. We’ve decided it’s the hottest park because it’s all asphalt and not to many trees or green areas. The heat just beats on you there so we have learned to go there really early and get out before the brutal afternoon heat.
But honestly no time is a bad time at WDW!