From the South, via the Taconic and Route 9:

Take the Taconic north to I-84 west.
I-84 west to Route 9 north, exit 13.
Route 9 north for just under 5 miles to Myers Corners Road (County Road 93). This is a  right hand turn just before a Mobil gas station that sits at the front edge of a Hannaford's parking lot. Note that this is the second light after the 7-11 Store.

Ketcham HS is about a mile down the road, on your left at the second light on Myers Corners Road.

From the North (via the Thruway and Route 9)
Take the Thruway to the New Paltz exit.

Turn right on Route 299 east until it dead ends on Route 9W.

Turn right on 9W going south until the entrance to the Mid-Hudson Bridge going toward Poughkeepsie. Cross the bridge and take the first right onto Route 9 south. Be careful of the left hand merge.

Route 9 South for about 8 miles to Myers Corners Road (a left hand turn, just past the Goodwill and Hannaford stores and the Mobil gas station on your left).

Ketcham HS is about a mile down the road, on your left at the second light on Myers Corners Road.