A photo from 1911 showing Chatham House school cadet corps who were briefly an OTC between 1908-11. The school closed in 1917.
Prior to 1908 the school cadets were affiliated to the 1st VB (later 4th Bn) Buffs but the cap badges appear to the RWK to my eyes.
http://www.michaelsbookshop.com/orw/id7.htm The original website photo is here which is easier to magnify.