Since 2007 pupils at Downe House have followed the Edexcel IGCSE Mathematics qualification.

The first 2 cohorts to take this qualification (2009 and 2010) were following the 2003 IGCSE specification from Edexcel which was not accredited by the Department for Education and therefore could only be offered by independent and international schools.

In 2009 Edexcel updated the IGCSE specification and this was followed by candidates taking the qualification in 2011. The new IGCSE specification is accredited and therefore recognised by the Department for Education when compiling their league table data. Approximately 20 pupils each year take IGCSE Mathematics a school year early which means that there are pupils in the GCSE class of 2011 who gained IGCSE Mathematics in 2010 after following the earlier specification. These candidates gained outstanding results (90% A*, 100% A* – A) but they are not acknowledged in the league tables published following the 2011 GCSE/IGCSE exanimations due to the change in accreditation.