Directions (from Rod): Take the Pebble Beach/17 Mile Drive exit off of Hwy 1.
When you get to the gated entrance to 17-Mile Drive, mention the fact that you're going to the bike race at the school and you won't have to pay the entrance fee. Follow 17-Mile drive about 6 miles, turn right on Stevenson Dr. and look for the signs for the Stevenson School (RLS).  The race will start at the football field.

More directions (taken from http://www.rlstevenson.org):
Driving from San Francisco and the Bay area:
           Take Highway 101 south to Prunedale. Exit Highway 156 to the Monterey Peninsula. After five
           miles, you will intersect with Highway 1 heading south to Monterey. Take the Pebble Beach
           /17-Mile Drive exit and follow signs through the intersection to the Pebble Beach entrance gate.

           Driving from the Los Angeles area:
           Take Highway 101 north to Salinas. Exit Highway 68 to the Monterey Peninsula. After 20 miles,
           you will intersect with Highway 1 heading south to Monterey. Take the Pebble Beach /17-Mile
           Drive exit and follow signs through the intersection to the Pebble Beach entrance gate.

           Directions to Stevenson from the Pebble Beach entrance gate:
            Proceed through the gate and bear to the left.  The drive from the Pebble Beach gate
to Stevenson School is approximately 2.5 miles. At every intersection, you will see
directional signs that say either Stevenson School or RLS. The campus is
           located at 3152 Forest Lake Road.