The slightly cheaper, slightly faster and slightly more complicated way (approx 1:40)
Take the NJ Transit train to Newark Penn Station
From there get off and switch to the PATH train to WTC (world trade center)
At WTC (which is the last stop), follow the (quite badly marked) signs to the 2/3 subway stop, and take either one towards Brooklyn.
Get off at the Nevins street stop.
The simpler way (approx 1:55)
Take the NJ Transit train to New York Penn Station
From there switch to the Brooklyn-bound 2/3 train
Get off at the Nevins street stop.
From the subway stop, or if you're arriving from within the city and want to take a different subway, here's a map of the area [Harriet Ross Tubman Ave and Fulton St are the same street!]. The A on the map marks the school at 1 Rockwell Place, Unit CB.