If you intend to re-use your poll, clear the responses from the poll before you present it again. You can keep a record of past responses by generating a report on each presentation of the poll. Generating reports can be done before or after clearing responses.
If the meeting is a recurring meeting and you do not want to use Poll Everywhere in future meetings, remove the Poll Everywhere app at the end of the meeting. You can also remove the app from any channels or chats you have added it to in the same way.
You can view the responses to single activities or run reports on a series of activities.
Clearing results will not impact your ability to generate reports.
If you ask your students to register, you can track their achievement: the number of correct and incorrect answers, their overall result as a percentage and you can generate a group rank.