If you have submitted the Service Book with your present school updated from all your previous schools, you should apply in plain paper for 10 years’ incremental benefit to the secretary of your present school. The HM will arrange for a meeting of MC which will approve your claim, if your service has been continuous and satisfactory and forward the same to the DI/s with necessary documents (i.e., your application, copy of MC Resolution, copy of Acquittance Roll showing your present basic pay etc.). The DI/s will verify the papers and issue an approval letter to the Secretary. The very next day of your first joining date will be the effective date of the incremental benefit.
You have two options- 1) If you take the benefit on April, 2015, your next increment will be on July, 2016,
2) You can take the benefit on July, 2015. In that case you will be eligible to have double increment on July, 2015.
But you should apply before when your your actual date of incremental benefit is due.