@ellythomas :
A keyword in your post is that you were "substituting" in a class. Students, who may be less self-regulated than most, may feel having a "substitute teacher" in their classroom opens a new door of opportunity for unbounded behavior. In the context of a substitute teacher, students may engage the idea there are no defined boundaries or guidelines; or for that matter consequences, so they feel empowered to "seize the day." If possible, I would consult the regular teacher on the classroom management guidelines she has in place and make the class immediately aware that I am supporting those same guidelines during the substitution period. I have found it useful to set, and/or modify the "state of the classroom" to a frame of positive reference and introduce myself, explaining my role, what I do in the school context, and assuring them, I am glad to serve as a support and guide during the teaching period. Education literature suggests the most effective way to manage a classroom is to serve as a "guide" for students and engage them in the best way they learn. In the short term, as would be the case with a substitute teacher, the opportunities are more limited. However, moving around the classroom, addressing students by name and making ourselves part of the environment often encourages them; especially those who may be disruptive because they are generally unprepared, and disengaged. Their poor behavior may be their method of accommodation. If so, developing a relationship, even short term, may be a key to success. Dr. Douglas Stewart
