Try one or more steps to reduce echo:

1. In Device Settings, under Mircophone test make sure that 'Auto Adjust Audio' is checked. It automatically sets the audio and reduces echo.

2. Right click in the class window to open up the context menu. Click Settings in the menu. Macromedia Flash Player Settings window opens up. Click on microphone icon and check 'Reduce Echo' option.

3. Uncheck boost in microphone device settings.

4. Use a headset and not desktop speakers.

If a class participant (may be an attendee or a presenter) is experiencing echo then all other class participants are required to make settings at their ends. Preferably, the presenter may transfer control to the attendees one by one and identify the system generating echo.