First and foremost, be sure to check the park's website to be sure there aren't any special events on the day you're planning.
Like you said, this is the prime time for school trips. Most schools will get to the park around opening and stay until 4-5pm. Thursdays and Fridays are the big days for school trips, so Monday-Wednesday will likely be your best bet. And even if you get unlucky and are at the park on a day with a bunch of school trips, it will still be less crowded than the average summer day so you'll still be able to get on every major coaster.
The other issue you run into is Kingda Ka and Zumanjaro. Until Zumanjaro opens, Kingda Ka will be closed during the week. Zumanjaro has begun testing but no opening day has been set (though it's been rumored that it may open next weekend, but again that's just a rumor). So you'll have to make a decision between skipping Kingda Ka and Zumanjaro in exchange for shorter lines, or waiting until they open (which a date still has not been set) and facing longer lines. If you'll be coming again this year it may not be an issue, but if this will be your only trip, it might be something to consider.
Hope that helps. Feel free to ask anymore questions!