In an email sent at around 11.30pm on Friday, the school said it had been notified of a new Covid-19 case.
"In this instance, the confirmed patient is a student in the Middle School in grade 9. Her sibling in Highlands Primary and both parents have all tested negative. The family is enforcing self-quarantine, and has been doing so since Thursday afternoon," the school said.
According to the US Center for Disease Control and Prevention, the symptoms of Covid-19 are similar in children and adults.
"However, children with confirmed Covid-19 have generally presented with mild symptoms. Reported symptoms in children include cold-like symptoms, such as fever, runny nose and cough. Vomiting and diarrhoea have also been reported. It is not known yet whether some children may be at higher risk for severe illness, for example, children with underlying medical conditions and special healthcare needs.
"There is much more to be learned about how the disease impacts children," it says on its website.