The effectiveness of a meeting can be measured in terms of its outcomes. If people don't follow-through on action plans, tasks and decisions after the meeting ends, then one needs to question the value of having a meeting in the first place. The leader is the single most important factor in follow-through. It's your job to be clear at the end of every meeting who is responsible for what and by when.
A leader can use these tools and techniques to achieve more effective follow-through after a meeting:
How to Lead Effective Meetings