Previous research has shown that high frequency lexical items, such as AWL words and formulaic expressions, may differentiate between texts written by expert and novice writers (Chen & Baker, 2010; Hancioglu, 2009), and that lexical features related to breadth, depth, and accessibility differentiate among texts from L2 writers of different proficiency levels (Crossley & McNamara, 2009, 2012; Crossley, Weston, McLain Sullivan, & McNamara, 2011). The current study compared the essays written by EAP students in response to either a cause or an effect writing prompt. As part of their EAP writing class, the students (N = 94) had two weeks to read six source texts and take notes to prepare for an integrative-writing exam. Students' essays were assessed by three raters using a holistic rubric, and five lexical features of their essays were analyzed: percentage of AWL word use, content word frequency, word familiarity, imagability, and lexical diversity. The results indicated that responses to the effect prompt were rated significantly lower than cause essays, contained more frequent and familiar words, and had a lower percentage of AWL words. However, there was no significant correlation between essay ratings and lexical features. Potential explanations for the findings and pedagogical implications are discussed.