"the girls could attend without the necessity of keeping strict purdah"

The word purdah means curtain and refers to the prevention of women from being seen by men or strangers.  Although it is associated with the Hindu and Islamic religions, it is usually a cultural tradition rather than a religious one.  Purdah can mean either complete separation of men and women (e.g. with the use of private women's areas such as a zenana) or the wearing of burqas and veils.