It is allowed for the man to lecture to the women in the same room
without a partition if all of the following conditions are met:
1) The women are wearing complete Hijjab (cover includes face, hands,
feet, etc..).
2) The women don't speak in a tempting voice.
3) If the instructor and the women are not being attracted to each
other and feel no (fitnah) desire.
It is better to have a partition between them because it is more pious solution for both the man and the women Plus,
the women would be able to dress in their comfortable way without Hijjab.
And Allah knows best