To get to Tenwek high school from Nairobi, board Transline Classic Shuttle that heads to Kisii at Afya Centre and alight at Bomet County. From Bomet, board a matatu that can get you Tenwek high school. You can also any Narok Shuttle that gets to Bomet county.
If you are using a personal vehicle then drive to Bomet County using the Narok route. Before you exit Bome town, take a right turn to Tenwek. It is about 6 km from Bomet town.