Classroom Culture

The issue I have been struggling with the most in my classroom this past semester (and year) has been investing my students and creating a positive classroom culture. Last semester, one of my science classes seemed to naturally create this type of culture because there were a few students leaders who were usually present in class and pushed the others forward. Without students taking on those leadership roles, however, I have had a difficult time creating and nurturing this type of classroom environment. Students are not interested in the class and seem to approach assignments as just something to finish rather than learn. The root of the problem in two of my classes seem to be young men who display aggressive behavior and anger at school.