Information on the history of the school may be found here:
Another of the Westminster scholars very narrowly escaped drowning on Tuesday, in one of the Robert Cockle-shell boats, which are so imprudently let out to them. There were two young gentlemen in the boat, and the eldest who fell overboard, was not more than ten years of age. The master of the school should interfere in this business, and put a total stop to any of the scholars going on the Thames, in any other manner than a waterman's boat, and at the same time attended by the waterman. This would do a double service. It would prevent accidents, and be the means of securing our nursery of seamen on the Thames, which daily diminishes for want of proper encouragement.
The Times (London, England), Thursday, Jul 03, 1788; pg. 4; Issue 1114