API Usage example of `https://getclever.com/developers/docs/`. You might run this in the `console` of any Chrome tab.

clever-sis-api.js

(function(){
  'use strict';

  function ajax(url, done){
    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.setRequestHeader('Authorization', 'Basic ' + btoa('DEMO_KEY'));
    xhr.responseType = 'json';
    xhr.onload = function(e){
      if(xhr.status === 200){
        done(JSON.parse(xhr.response), xhr.status, xhr);
      }else{
        done(null, xhr.status, xhr);
      }
    };
    xhr.send();
  }

  ajax('https://api.getclever.com/v1.1/sections', function(res, status, xhr){
    var sum, avg;

    if(status !== 200){
      console.log('Request failed with status code ' + status);
      return;
    }

    sum = res.data.reduce(function(sumSoFar, section){
      return sumSoFar + section.data.students.length;
    }, 0);

    avg = sum / (res.data.length || 1); // avoid Infinity

    result(avg);
  });

  function format(data){
    var rfixed = /(\d+\.\d{2})(\d+)/;
    return data.toString().replace(rfixed, '$1');
  }

  function result(data){
    console.log('The average number of students per section is: ' + format(data));
  }
})();