A four-minute interval protocol of eight rounds of 20 seconds all-out work and 10 seconds rest, from Izumi Tabata's 1996 study.
The original study used cyclists working at about 170 percent of VO2 max, which is genuinely maximal: the subjects could not complete the eighth round on some days. Done properly it is four of the hardest minutes in training, and almost nothing done in gyms under the name Tabata is done properly.
A 20-on, 10-off circuit of squats, push-ups and mountain climbers is a fine conditioning finisher, but it is not the protocol and it will not produce the study results. Calling it Tabata sets a client up to expect an effect the session cannot deliver.
If you want the real version, use one cyclical exercise the client can go truly maximal on with no technique risk: an assault bike, a rower or a stationary bike. Once a week is plenty, and never before a heavy lower-body session.