Teach got a new skill during his strengthening that lets him heal the party for a maximum of 2000. But if the receiver is female, it doubles to 4000.
Fionn, David and Kojiro seem to be trying to get the bonus to no avail. Paracelcus has the system confused. And the system, like everyone else doesn't care with regards to Astolfo and Rama since they're cute. The game does not actually give Rama or Astolfo the bonus, in fact Astolfo is immune to gender dependent skills.