Half a dozen teenage girls sat in the small, windowless classroom in the ultra-Orthodox Jerusalem neighbourhood of Mea Shearim learning — for the first time — about sex.

“You must not move too much, lest you distract your husband. You must think of this as a holy act,” repeated the teacher with a stern but kind look.

The young women, aged 16 to 20, looked terrified. All are about to enter into arranged marriages with men they met through their rabbis or parents.

For most, the class is the first introduction that they have had into the basics of male and female genitalia, let alone the workings of sex, or, as they call it: “How a baby is made.”

“It’s a lot, but it’s important