One of the critiques of proficiency as defined by scales, such as that of ACTFL, is its lack of grounding in linguistic realities. Measures of complexity, accuracy, and fluency provide a route in which proficiency can be quantitatively measured by identifying linguistic correlates (see Brown et al., 2017; Long et al., 2012). This project aimed to identify the linguistic correlates that distinguish L2 Spanish writing at intermediate-high and advanced-low proficiency levels as defined by the Language Ability Self-Evaluation Resource. Forty writing samples comprised the data. Measures of lexical complexity (density and diversity), syntactic complexity (mean length of T-unit, number of clauses per T-unit, average length of error-free T-unit), and accuracy (ratio of error-free T-unit, number of errors per 100 words) were used to analyze the samples. Findings suggest that accuracy is the linguistic feature that best distinguishes intermediate from advanced proficiency in L2 Spanish writing. The implications of these findings for research and pedagogy are examined.