Similar query was discussed in this link, pl.browse and know the position-
What your school following is not as per the Maternity Benefit Act. As per this stipulation 26 weeks (6 months) of paid leave has to be granted to the pregnant employee. Pl.point out this act position to the management for an amicable redressal of your grievance.
Pl.read the discussion in this link also -
The Maternity Benefit Act is applicable to all private establishments also including educational institutions except those covered under ESI act whom maternity benefits under ESI schemes are applicable. If you would need more info on this subject pl. use the search option in the box at the top and other links provided on to your right on screen.