Try
onComplete: function(rs){
var rs = JSON.decode(rs);
var el = new Element('tr');
var start = new Element('td', {'html': rs.start}).inject(el);
var end = new Element('td', {'html': rs.end}).inject(el);
var student_count = new Element('td', {'html':
rs.student_count+'Student/s'}).inject(el);
var price = new Element('td', {'html': rs.price}).inject(el);
el.inject($('schedules'));