From

[Your Name],

[Your class & section],

[School Name],

[City].

To

The Class Teacher,

[Your class & section],

[School Name],

[City].

Subject: Request for leave of absence 

Respected Sir/Madam,

As I am suffering from fever, I will be unable to attend the school for [number] days, from [start date] to [end date]. I request you to consider my absence as leave. 

                                                         Thanking you,         

    [City]                                                                                          Yours obediently,

    [Date]                                                                                         [Your Name]