I've gone down the last two years during that time frame. The parks were hit and miss on weekdays, for issues I'll address below. The weekends(or at least Saturday as I wasn't there on Sundays) were extremely busy. On weekends, get there early, use fastpass, and stay late to minimize wait times.
While most California schools are still in session during that time period, some neighboring states are out of school, so expect the park to be busier than in May. You may also have to contend with local schools having field trips in the park. This will usually impact crowds, but even more tricky can be the herd mentality that seems to envelop many of them. In other words, they'll stand around in the middle of a crowded walkway and debate over what they're going to do next, all the while not realizing that it's incredibly difficult to move around them.
In all fairness, not all school aged guests on field trips act this way, but enough do that it becomes something you have to deal with.
