De Coning, 52, had suffered a heart attack before 2pm last week Thursday at Hoërskool Birchleigh in Kempton Park, according to Kempton Express.
A close family member told the publication that De Coning had been writing something on the board when she suddenly stopped and complained that she was not feeling well.
De Coning, who had been in the teaching profession for 30 years and taught at Laerskool De Aar in Kimberley before joining Hoërskool Birchleigh in 1987 as the grade 8-12 maths teacher, later died.
A memorial service will be held at the school today, with a funeral service tomorrow at 2pm at the NG Moedergemeente Church in Kempton Park.
This had not been the first incident where a teacher died in front of their pupils.
In 2011, a primary school teacher was brutally hacked with a panga in front of his class in Matlala, near Polokwane, Limpopo.
The 53-year-old man had been teaching at the Masehlong Primary School when his brother allegedly walked in and attacked him. The teacher was taken to hospital, and died shortly after arriving, according to media reports.
In 2007, a Grade Two teacher was shot dead by a balaclava-clad gunman in front of her pupils at Niyona Junior Secondary School in Mount Frere in the Eastern Cape.
The teacher had been hit in the head and twice in the neck. She died instantly.
The results of the 2012 national school violence study revealed that violence in schools remained prevalent.
According to the study, about 52.1% of educators had been victims of verbal violence, while 12.4% were victims of physical violence and 3.3% victims of sexual violence perpetrated by pupils.