Male Teachers in Girls' Schools

Beis Yaakov, from its inception, had female and male staff members.  Over the years it has always had male teachers in addition to the female staff.  Various high schools and seminaries have become associated with their male principals such as R' Mordechai Miller a"h of Gateshead, R' Binyamin Steinberg a"h of BY of Baltimore, Rabbis Teichman and Greenberg of BYA, Rabbi Aisenstark of BY in Montreal, etc.

With two recent seminary (in Israel) scandals that I know of, I've been wondering about this policy of male staff members having such a great involvement with female students.  Chassidishe girls' schools do not have male teachers.  They may have a male guest lecturer for a special occasion; otherwise, men are not interacting with the girls on a regular basis in the classroom, learning their names, marking their papers, answering their questions, etc.

Why are male teachers and principals deemed necessary in BY types of schools while Chassidishe girls' schools do not hire them? Are the Chassidishe girls losing out by not having male teachers and hashpa'ah? If not, why do BY schools have them, and if they are, is there a way to have male teachers while ensuring the utmost decorum and distance?

I'd like to hear what R' Wallerstein, founder of Ohr Naava and related girls' institutions, has to say about this!