Webex in the Classroom

I need help finding the proper microphone for classrooms in my county school system. We've setup a distance learning program for Spanish and Nursing classes for the three schools in the system. One school is the host and the other two are the receiving sites. Our Spanish classes are having the most trouble with clarity when the teacher speaks and the children respond to his questions. We've tried both the built-in mics on Macbook and ConferenceCam, but it sounds terrible from both the host and receiving ends.  I'm looking for a USB microphone(s) that will help with my problem. I've looked at products from Blue microphones and Audio Technica. This is the equipment we have in place now:

Macbook Pro 13" or 15"(Built-in mic on laptop)

iPad 2 (For Document Cam and Mobile Cam)

Logitech HD  BCC950 Web Cam (Built-in mic)

BenQ EP5920 HD Projector

Speakers with Subwoofer

HD Projector Screen