From the marina to get to the school all you have to do is take the fourth turning on the right and carry on until you see the school on the left.
From Sam's house: Turn right and continue along Ocean Boulevard. Keep going past Grant Street and turn right at the next possible turning after that, and then continue up that road (Sherman Avenue). all the way.The school is at the end.
From Astrid's house: Turn left at the first turning out of the avenue, then right and keep going until you reach Sherman Avenue, and then turn left and follow the road until you reach the school.
In Gone the school is where the kids spot the first disappearances. In Lies it may have caught fire when Zil threw the cocktails and lighters. It was destroyed by Gaia during her final attack on Perdido Beach, killing several kids sheltering inside.