this dream denotes your arrival at the 'next stage' of development.
you've completed your learnings, and were prepared to return the texts.
however, you've had 'extracurricular' lessons, which appear in the form
of that "graffiti"... and you would be the best teachers, for the next
batch of students to learn from. the directive to "spit out the gum"
was meant to prepare you for 'speaking your truths' unimpeded, and
a subtle way of telling you to "grow up and act your age".