设计任务：请阅读下面学生信息和语言素材，设计20分钟的英语写作教学方案。教案没有固定格式，但须包含下列要点：
●teaching objectives
●teaching contents
●key and difficult points
●major steps and time allocation
●activities and justifications
教学时间：20分钟
学生概况：某城镇普通中学高中二年级学生，班级人数40人。多数学生已经达到《普通高中英语课程标准（实验）》六级水平。学生课堂参与积极性一般。
语言素材：

There is an increasing number of school violence happening recently which have exerted terrible influence on our school life.What can we do about it?Please write a passage of at least 120 words titled with "How to improve school safety?"
Key words:campus security guard