From the M55, follow the signs towards the airport. Just before the airport where the turn off for Morrisons / Curry's / PC World is turn right into St Annes Road. Its a good way up there but after going under the only bridge on that road it is on the left.
From other directions the school is half a mile inland from the Pleasure Beach. If you went through the tunnel under the Pleasure Beach that goes from the prom (Watson Road) and continue until you get to the same bridge mentioned above, turn left to the school.
Once you know the way, there are quicker but more complicated routes.