I rather dislike the idea of graded classes and like to work with mixed groups for at least some sessions, this gives the new dancer a chance to see what is being aimed at and the more experienced a chance to revisit and revise their technique.
Working in lines for part of a workshop can work well, the dancers can decide where they want to be and so can have someone to follow if necessary.
Try to give everyone a go at dancing on their own at some time, this can be very formal taking turns along the line, picking up the music in turn without missing a beat, (this is how Tap Dancing is taught), it can be a daunting but valuable exercise particularly when working with a Dance Team. I think that taking turns in this way is preferable to drilling which is both a boring and tedious, as taking turns engages everyone in listening and counting as well as doing and performing the step/s.
Try to vary activities, work on bits of things: work in pairs and small groups to learn new steps and dances. Most of all encourage the dancers to feel good about themselves and the group: ask yourself often - Why am I doing this, who is it for?