Unless you're there during the school day, you'll see the long west wall of Ochoa School from a distance... you might want to bring binoculars. It's covered end to end with murals.
We're looking from 7th Avenue between 25th and 26th Streets... click for a bigger view (use your browser's "Back" button to come back):
Here's a part from near the middle of the wall.
Update (October 23, 2012): don't miss the long mural on the east side or the north-side mural by muralist David Tineo and students.