Say "sentence diagramming" to people of a certain age, and one gets different reactions. Say it to most college students, and one gets a blank look. But not from the 24 students in Lucy Ferriss's "Constructing Thought," a half-credit course in the English department at Trinity College. They know how to diagram a sentence--and they are passionate about it. This article describes the course's main event, a sentence-diagramming "slam." Two teams will compete to see which one can, in 45 minutes, best diagram a 100-word sentence crafted by the other. Their lessons have been building toward the slam all semester. A tall woman with a commanding voice, Ms. Ferriss, 55, is the reason these 19- to 21-year-olds are so excited about diagramming, a method of teaching English grammar that fell out of favor when she was still in middle school. Her boundless enthusiasm for the structure of sentences, along with her high standards, has infected her students with a zeal to get it right. When completed, the phrases and clauses assembled by her students will form intricate, branching diagrams along each blackboard, like a delta or a graceful, fallen larch.