In this descriptive linguistic study, the lexico-grammatical complexity of placement and exit English for Academic Purposes (EAP) student writing samples was analyzed using corpus linguistic methods to explore language development as a result of student enrollment in the EAP program. Writing samples were typed, matched, and tagged. A concordance software was used to produce lexical realizations of grammatical features. A comparison was made of normed frequency counts for nine phrasal and clausal features as well as raw frequencies for type to token ratio (TTR), average word length, and word count. In addition, the contribution of variables such as advanced grammar and writing course grades, LOEP scores, and the number of semesters in the EAP program to the English Learner's (EL) lexico-grammatical complexity found in exit essays was also examined. Twelve paired parametric and non-parametric analyses of lexico-grammatical variables were performed. Dependent t test results showed that normed frequency counts for such features as pre-modifying nouns, attributive adjectives, adverbial conjunctions, coordinating conjunctions, TTR, average word length, and word count changed significantly, and students produced more of those features in their exit writing than in their placement essay. Non-parametric Wilcoxon test indicated that such a change was also observable with noun + that clauses. The frequencies of verb + that clauses and subordinating conjunction because, though non-significant, actually decreased. A split plot ANOVA allowed to see whether a change in above mentioned statistically significant lexico-grammatical features could be attributed to grammar instruction in EAP 1560. The results showed that there was no statistically significant difference between those who took EAP 1560 class and those who did not on pre-modifying nouns, coordinating conjunctions, TTR, average word length, and word count. On the other hand, those students who did not take EAP 1560 class had higher counts of attributive adjectives but lower of adverbial conjunctions, both statistically significant results, than those students who took the class. Lastly, five multiple linear regression analyses were conducted to predict frequencies of exit pre-modifying nouns, attributive adjectives, noun + that clauses, adverbial conjunctions, and TTR from EAP 1560 and EAP 1640 grades, LOEP scores, and the number of semesters students spent in the EAP program at SSC. The only significant regression analysis was with TTR, and 28% of its variance could be explained by the independent variables. LOEP Language Usage score was the only significant individual contributor to the model. Even though exit adverbial conjunctions were not predictable from the chosen IVs, LOEP Sentence Meaning score proved the only significant contributor to that model. The results indicate that compressed phrasal features are indicative of higher complexity and EL proficiency, while clausal features are acquired earlier and signal elaboration, as previously described in the literature.