Green’s Dictionary of Slang

topping school n.

a brothel.

1653		Mercurius Democritus No. 82: Two Ladies of the Night [were] presently by an old Quack [...] carry’d into a toping school.
1707		N. Ward London Terraefilius III 22: Her [i.e. a madame] most Topping School is among the Meeting House Allies, in Moorfields, [...] That the Saints may kill Two Birds with one Stone; and tumble out of the School of Piety into that of Debauchery.