Shall we revisit the fantasy aspect? It seems your looking for conflict, and this can be gained within a fantasy realm, which could offer more flavor than a modern realm (at least in my opinion). The society in which this school hides from and recruits much of its students from can see sex as something offensive and actively attempts to squash any like the school.
Or the society views sex as more than acceptable, however, does not accept anything other than simple vannila; I.E, no lesbians/gays, no bi-sexuals, no bondage, no master slave, nothing out of the plain old simple man/woman missionary position/and or a few other acceptable positions on the bed within the bedroom. Having the society accept sex would make the girls coming into the school less likely to rat it out as they would likely be seeking more fulfillment or have a strong desire to learn more about sex. There can still be drama, this is not a hard and fast, as some girls might rat them out or what not.
So that is where the girls all much have a spell(s) cast on them for security purposes. It can inflict pain perhaps, immobilize, wipe memories if needed, etc.
Now the truly fantasy aspect could add creatures to mix, or things that just couldn't be hidden in a modern world. Like how could one hide a Dragon in the modern world for long? How could a magical occurance stay hidden for long? Perhaps this occurance is not localized but happens throughout the land in certain places. What about plants that do not exist in a modern world that could be used for various reasons. What about minotaurs or pixies; I can think of devious or creative uses for those little pixies.
These magical occurances can cause arousal, loss of memory short/medium/long term or in a rare occasion permanent, they can be summoning portals, mirrors into ones soul and or desires, perhaps they can be power sources, the uses for them are limitless.
Being fantasy would allow for different race fetishes to be included to. Perhaps someone is a sexy half drow elf, or has dragon blood from a long diluted ancestry, perhaps strongish demon blood which gives her a temper, the teachers could be a succubus perhaps, one who isn't just totally evil and actually likes the prospect of personally turning her students into salivating, writhing, screaming piles of flesh begging her for more until finally they black out and wake up in their dorms...
There is more than enough room for conflict, I can see several ideas already. If the school has a demon as a teacher that alone could earn the school death threats and such from scared parents and or the cities ruling body. Mayne this place does not like certain species? There is so much more...