Cornish has two elder sisters, who were both head girls at school. Unlike her academic sisters, Cornish has stated she was "never really that good at anything". She said, "At school they were like 'oh, you're a Cornish girl' and they kind of expected me to be the same as my sisters. Give me something to draw or an outfit to pick for someone, or hair, make-up, acting, write a song, I'm fine with it, but anything to do with sums – it was never my thing. " She also said she never based her intelligence on her exam results. She also said she was always good at singing and it was her "thing". In 2003, aged 15, she won Best Pop Singer in the TV show Britain's Brilliant Prodigies, performing as Jessica Cornish. At the age of 16 she began studying at the BRIT School and at 17 she joined a girl group named Soul Deep. She graduated in the class of 2006 along with singers Adele and Leona Lewis. At 18, she claims she suffered a 'minor stroke. ' Regarding her choice of the stage name "Jessie J", in an interview with the Daily Mail, she is quoted as having said "to be honest, there's no real reason for the 'J' in my stage name".