Kallah teachers are entirely unregulated, and the quality of their classes vary in content and in delivery.
But that's not the biggest problem...
The explanation is prescriptive – usually with a line drawing of the male and female form. It comes as a shock to many women, particularly those within the Chasidic community.
At this point there is no opportunity to discuss it with the prospective groom, to find out what works for you both, or to back out, especially if the binding 't'noim' document was signed at the engagement party.
If the bride didn’t know about sex until this point (and many don’t), then in agreeing to the engagement she has not agreed to sex. She cannot agree to sex within the marriage without knowing she is agreeing to have sex with him, as well as marriage.
There's another element. Charedi Kallah teachers often insist that a marriage must be consummated on the wedding night.
In practice, this means that the first experience of sex follows shortly after being told about it.
Further, many Kallah teachers will tell their students that they have the right to say no – but if they say no, and their husband ‘spills his seed’ or ‘goes elsewhere’, that sin is on them.