To start 3 players attack the 2 defending players on the other side of the court.
When the defenders collect the rebound they then attack the other basket against the 1 player that took the shot.
(Drill the restarts with all 3 players who finished the previous run through on the offensive).
Aim of this practice:
Good team defence is five players guarding the ball, not five separate one-on-ones. The shell drill is where that starts, so here is how to teach help-side positioning and rotations from the first week of the season.
Rebounding is the least glamorous thing in basketball and one of the most decisive. It is also almost entirely a habit, which means it is entirely coachable.
Good spacing is only the start. The best modern offences teach players to attack the defence's rotations and play in a permanent 4-on-3 - here is how to coach that read.