From Concord Center, take Lowell Road toward Carlisle. (There is a sign.)
Take Lowell Road all the way to the rotary at Carlisle Center. You'll pass the Middlesex School on your right. Carlisle is about 3 miles from there.
As you approach the rotary, you'll see a hill on the right - this is School Street, and you should take this right, going up the hill.
The first left off School Street is Church Street. (There's a church on the corner.) Take the left onto Church Street, then a quick right into the school's parking lot. Walk up the stairs, cross the bus plaza and walk up the second set of stairs to the building level. Buildings are clearly marked.
All visitors must check in at the main office in the Spalding Building.