How I handle tardiness has a lot to do with the kind of meeting that is occurring. I once inherited a large twice-a-week update meeting from my boss. He was notorious for being late. He had run the meeting for about 3 months and then it was mine to run. By the time I got it, it usually started 10-15 minutes late and ran 3-4 hours (2 hours longer than scheduled). There were well over 50 people in attendance. People would show up late in part because they knew the piece they were actually interested in would not get started for at least an hour — so they would show up an hour late. With that size of a group it was not going to be solved by a one step process. Also tardiness was just one symptom of the overall group dynamic issue. We also had problems with surprise agenda items where one person would be ready to talk, but no one else would be prepared.
My steps to solving the group’s problem was to first always publish an agenda and stick to it. No one was allowed to add a new topic during the meeting. Second was to grant speakers an allotted time and then cut them off (politely) and tell them that that they will have to come up with a faster way to explain their issues or create a subset meeting where they could go into more detail. Third, we finished on time. I refused to backtrack during the meeting and catch anyone up on where we are. If you are late, you just have to wait for the meeting notes to come out to find out what was discussed. Once people realize that you are not going to waste their time in your meeting and that real things are going to happen, they tend to make it a little higher priority. Tardiness rapidly became less of a problem.
It took about 6 rounds of this meeting style for everyone to get on board. The end result is that we got through those meetings in 45 minutes. Everyone knew what was going on. In fact several people remarked that they felt better informed in 45 minutes than they used to feel after the previous 4 hour marathons.