It is a non-geographic Constituent Body (CB). There are a few other non-geographic CBs such as the Students RFU and the Army RFU but most CBs are geographic ones: Kent County Rugby Football Union is a geographic CB.  As it is a CB ERFSU has two representatives on the RFU Council as well as membership of some committees of RFU. 

ERFSU's objects (defined in the Memorandum of Association which constitutes its structure) are to administer, foster, encourage, extend and control Rugby Union Football for the moral, mental and physical development of school boys and girls attending schools within England (which includes the Channel Islands and the Isle of Man).

Kent Schools' RFU is a Constituent Schools' Union (CSU). It is a constituent member of ERFSU and has representation on the ERFSU Committee. Its members are eligible to be appointed to ERFSU posts and committees and over the years it has been actively involved in that way.