1
My son has temperature, so he can’t go to school.
My son has a temperature, so he can’t go to school.
In British English, have a temperature or run a temperature means to have a higher body temperature than normal because you are ill: ‘My son has a temperature.’
Use a before temperature with this meaning.
2
When I was ill, I had 39 degrees of fever.
When I was ill, I had a temperature of 39°C.
When I was ill, my temperature was 39°C.
To give the exact measurement, use have a temperature of + number or someone’s temperature is/was + number: ‘She had a temperature of 38°C.’ ‘Her temperature was 38°C.’
Do not use degrees of fever.
See FEVER