How To Write Letter For Issuing Experience Certificate To School SINCE I HAVE LEFT THE SCHOOL?

To
The Directress,
ABC School,

Respected madam,
Sub:Requisition for experience certificate
  As I handled, grade 6 and grade 7 (I.T) and I have completed my 1.5 2 years approximately years ofd experience.Kindly grant me experience certificate.
  Thanking you.
  Yours truly,
  aaa.