The information requested is not recorded in the format required.
Student leave is granted for the duration of the course, therefore can vary greatly. It is not possible to cross reference the extension data for 2006 against the initial leave to enter data for any one previous year therefore it is not possible to provide data in terms of a percentage.
However, data of student visa holders who extended their leave to remain during 2006 can be found in the Home Office Command Paper “Control of Immigration: Statistics United Kingdom 2006” pages 56 and 58 table 4.1. A copy of which is in the House Library.