The aim of this pre-experimental study is twofold: (1) to investigate the comparative effectiveness of individual, pair, and group writing conditions in L2 writing classes, and (2) to explore students' perceptions about each of these conditions. The participants were university-level Turkish EFL learners studying in the English Preparatory Program of a state university. The data for investigating the effectiveness of these writing conditions came from in-class paragraph writing tasks whereas students' perceptions were investigated through an open-ended questionnaire and semi-structured focus group interviews. The quantitative data were analyzed by running descriptive statistics analysis, Wilcoxon signed-rank test, and the Friedman test, and the qualitative data were content analyzed. As the findings indicated, when the participants wrote in groups they outperformed those who worked individually or in pairs regarding the (a) fluency, (b) accuracy, (c) complexity, (d) length, and (e) overall score of the paragraphs. Besides, perceived advantages and disadvantages of both collaborative writing (i.e., pair and group writing) and individual writing were pointed out by the participants. Based on the findings, some pedagogical implications and suggestions for further research are presented. (C) 2019 EJAL & the Authors. Published by Eurasian Journal of Applied Linguistics (EJAL).