The dream in which you are being in the class, but in reality you are already an adult, shows some memories that are very important to you from your childhood. If you are child, it is very normal dream because of the time you spend in the school.
Dream dictionary: Class (school) dream meanings
…(Behind | Posterior | Rear side) In a dream, the back of a human being represents what people hold for him of praises or blame, acceptance or rejection, honor or humiliation, or it could represents one’s debts. Seeing the back of a human being in a dream also means following his tracks or practices. If a positive look manifests therein, such as a sweet fragrance or the emergence of a radiant light, or if it turns into iron in the dream, it signifies one’s gratitude regarding his own condition. In a dream, the rear side of the human being represents his outward appearance or what renders the human being accept- able, or it could represent his garment, an ostentatious person, a show of grandeur, pride about one’s social class, a show of being wealthy, the surround- ings of one’s house, the outskirts of a town, the outer display of…