Are belts necessary?

No, not really.
However, any martial art requires:

1. A syllabus
   - defining the components that will enable a student to achieve the objective
   - a path leading to the knowledge
   - a scheme of work
   - how the student will proceed
    
2. Topics
   - breakdown of the syllabus into modules of information
   - logical building blocks
   - small steps along the path
   - teach according to the students ability to learn
    
3. Discrete lessons
   - a lesson is an opportunity to explore a given skill
   - examples must be provided
   - thought-provoking
   - stimulating
   - encourage enthusiasm and participation
   - engage the student
   - allow for different ability levels
    
4. Proof
   - examinations, tests, grading
   - pressure-testing
   - an increasing scale of hardship

Without these, the material might potentially be taught in a haphazard, piecemeal, random manner.