You should get your GPF a/c no. from your School. If School’s GPF a/c no. is xyz123 then staffs a/c nos. will be like xyz123/01, xyz123/02, … (or may be in other way).
Calculation of Interest
At first please buy a P.F Ledger
If interest rate is uniform i.e at present 8.6%
then first you add all Lowest Balance (may be col. 8 in P.F Ledger). Let this is be 100000/-
Then your 1 yr. Int. = (100000*8.6)/1200.
Note: Lowest Balance is comes from Opening Balance+Amount deducts in one month and so on continue