In many ways, the “messy room” is emblematic of the adolescent age. Usually beginning in early adolescence (years 9 – 13) as a function of personal disorganization brought on by more growth change than the young person can easily manage, this state of physical disarray quickly attracts parental attention.  
 
To parents (and particularly to step parents), the messy room can feel like an affront to domestic order, representing “disrespect” for the more neatly kept home they value. Their expression of disapproval in response usually becomes an affront to the adolescent who sees a power issue worth fighting for. It represents “personal freedom” to live on his or her own terms. 

Thus a specific disagreement over order becomes a symbolic struggle over who’s in control. “It’s my room! ” declares the adolescent. “I should be free to live in it any way I want!” “Wrong,” counter the parents. “It’s our home, and you will live according to the standards of household order that we set!” So the battle lines are drawn for a conflict of mess up vs. clean up that can unfold over many years.   For the adolescent, there can be a lot at stake in asserting the right to the messy room – issues about independence, individuality, and opposition to parental rules. As a statement of independence, the child seems to say: “I should be able to live in my own space in my own way!” As a statement of individuality, the child seems to say: “I am now a different person than I was as a child!” As a statement of opposition, the child seems to say: “I’m going to live MY way, not your way!”  
 
So, do you want to let the messy room go? Do you want to just accept it as a developmental byproduct of this more assertive and rebellious age? Or do you want to make a supervisory response instead? Parents who let the matter go tend to do so to their cost. They adjust to what they don’t like and then blame the adolescent for their unhappiness. Better to hold themselves responsible for not adequately supervising what matters to them.