Why does my solution work in the console but not the browser?

# The dictionary will be something like:
# {'Jason Seifer': ['Ruby Foundations', 'Ruby on Rails Forms', 'Technology Foundations'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Often, it's a good idea to hold onto a max_count variable.
# Update it when you find a teacher with more classes than
# the current count. Better hold onto the teacher name somewhere
# too!
#
# Your code goes below here.
def most_classes(teachers):
  #storage variables
  max_value = 0
  #for each teacher key in the teachers dictionary
  for teacher in teachers:
    size = teachers[teacher]
    if size >= max_value:
      max_value = size
      max_teacher = teacher
  return (max_teacher)