The school was inspected in 2012.
From the ISI web site:
Wimbledon Common Preparatory School was not accredited to one of the ISC Associations* at the time of its inspection, which was carried out in order to establish whether the school met the accreditation requirements.
*The Associations are:
The Council of British International Schools (COBIS)
The Girls' School Association (GSA)
The Headmasters' and Headmistresses' Conference (HMC)
The Independent Association of Prep Schools (IAPS)
Independent Schools Association (ISA)
Society of Heads of Independent Schools (SHMIS)