George Salter Academy is closed this week to years seven, 10, 11 and 12 students.
In a statement on their Facebook page on Sunday, the school said: "Unfortunately, due to low staffing capacity because of the Covid-19 pandemic we have had to take the decision to close the academy for year seven, 11 and 12 students only for this week.
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"There are currently some year 10 students who are not self-isolating for whom we are closed until Wednesday. We intend to revisit the decision ahead of any possible return for these students. In the meantime, the academy will also remain closed for all year 10 students until further notice.
"I have not taken this decision lightly and would only do so when no other circumstances would permit the safe opening of the school for all students."