[eng] The aim of this study is to analyze the effects of proficiency level and time distribution of instructional hours on adult second language learners' written production. Two English as a foreign language programs were considered: "regular" and "intensive". A total of 292 writing samples from 83 intermediate-level learners and 63 advanced learners were analyzed by means of different measures of fluency, complexity, and accuracy. Additionally, a group of native English speakers (N = 29) was included to provide baseline data. The results of the statistical analyses suggest positive effects of time concentration for the development of fluency and lexical complexity at the intermediate level. The results of the students at the advanced level are discussed on the basis of their performance with respect to the native English speakers.The aim of this study is to analyze the effects of proficiency level and time distribution of instructional hours on adult second language learners' written production. Two English as a foreign language programs were considered: "regular" and "intensive". A total of 292 writing samples from 83 intermediate-level learners and 63 advanced learners were analyzed by means of different measures of fluency, complexity, and accuracy. Additionally, a group of native English speakers (N = 29) was included to provide baseline data. The results of the statistical analyses suggest positive effects of time concentration for the development of fluency and lexical complexity at the intermediate level. The results of the students at the advanced level are discussed on the basis of their performance with respect to the native English speakers. [spa] El objetivo de este estudio es analizar el efecto del nivel de competencia lingüística y la distribución de las horas de instrucción en la producción escrita de estudiantes adultos de segundas lenguas. Se han considerado dos programas de inglés como segunda lengua: "regular" e "intensivo". Se han analizado 292 redacciones de 83 estudiantes de nivel intermedio y 63 de nivel avanzado utilizando diferentes medidas de fluidez, complejidad y corrección. Además, se ha incluido un grupo de nativos anglófonos (N = 29) como referencia. Los resultados de los análisis estadísticos sugieren un efecto positivo para la intensidad en fluidez y riqueza léxica para los estudiantes de nivel intermedio. Los resultados obtenidos por los estudiantes de nivel avanzado se discutirán en relación a la producción escrita de los nativos.