The last week in Aug. will probably be crowded. Schools in So Cal don't start again until after Labor Day. It will also probably be very hot. Late Aug. and early Sept. can easily be in the 90s. If you can work it out Nov. will be a much better bet.
That being said, if you can only go in Aug. than you should do it. I am going to WDW in Aug. because that is when I can make it, crowds, heat, hurricanes and all!
Melissa