Halacha requires placing a Mechitza (separation) between men and women in the synagogue; according to Rabbi Moshe Feinstein (Russia-New York, 1895-1986), this requirement constitutes a Torah obligation. Rabbi Feinstein rules in a number of his responsa printed in his work "Iggerot Moshe" that the Mechitza must stand at least eighteen Tefachim or approximately 54 inches tall, such that it reaches the shoulders of an average woman.
Rabbi Feinstein also wrote that a Mechitza should be present at any gathering attended by men and women, such as weddings and other social functions. The prophet Zecharia foresees the funeral that will be held when Mashiach arrives for Mashiach Ben Yosef, and he declares, "The land shall eulogize each family by itself: the family of the house of David by itself, and their wives by themselves" (Zecharia 12:12). It emerges from the Talmud's discussion in Masechet Sukka (52a) that Mechitzot will be erected to separate the men and women during this funeral. Rabbi Feinstein notes that if Mechitzot are required to separate between men and women at the solemn occasion of a funeral, then we should all the more so require Mechitzot at more festive social gatherings.
Rabbi Feinstein does, however, make an exception in cases of a weekly Torah class offered to men and women, if there is concern that many women will not attend if a Mechitza is used. In such instances, Rabbi Feinstein rules, in the interest of disseminating Torah to as wide an audience as possible, we may suspend the Mechitza requirement if otherwise many women would not attend, provided, of course, that the men and women are seated separately.
Summary: A Mechitza in the synagogue must stand at least 54 inches tall. A Mechitza should be used to separate men and women in all social venues where men and women are in attendance, such as weddings, funerals and Torah classes. If, however, there is concern that many women will not attend a Torah class if a Mechitza is used, then it is permissible to conduct the class without a Mechitza, provided that the men and women sit separately.
