Release from Old School to Join a New One

Is it possible for my school authorities to prevent me in doing so by not releasing me in due time?

I can not understand your question.
1) If you want to join in new school, then you will submit your resignation and apply to get release order.
2) If you do not want to join in new school, then there will be no problem for taking NOC.

I think you have submitted your resignation to your H.M./T.I.C. Your H.M./T.I.C. will inform it to the M.C..M.C. will call a meeting with minimum 7 days interval. In this meeting, they will take a resolution to give you release order. In between this time you will inform your new school accordingly and fix the date of release so that you should join your new school in no gap. ( Suppose, you will take release order on 5/11/13, try to join in your new place on 6/11/13. There will be no problem in future. Otherwise the gap of the days,i.e. max.5 days, you will not get salary.
*** You need the following PAPERS related to your service and your service continuation:-
1) Copy of the M.C.Resolution accepting your resignation,
2) Release Order indicating No. and Date of the M.C.resolution,
3) Service book (Counter signed by the D.I.of schools)
4) Last Pay Certificate (Counter signed by the D.I.of schools),
5) P.F. withdrawal accrued with interest till date,
6) Others necessary documents and papers as required.
Good luck .