Start with quarter notes, play 4, rest 4, while marking time and on the move. The rest allows recovery time and time for you to deliver short, precise instructions while keeping their feet moving. Always use the metronome and define what part of the foot hits the ground on the beat. Exaggerate the impact of the heal in the ground on the beat. Work to more advanced rhythms as they master the easier.
It would be interesting to know their rhythmic and tempo control during concert band. One tends affect the other.