Thi s study investigated, using think-aloud protocol, what L2 learners focus on, notice and uptake in a series of English writing task and how this cognitive process is affected by their English proficiency. Nine Korean middle school students were engaged in a three-stage writing task, which consisted of the compos ing stage, the stage of comparing their own text with a reformulated version, and the revising stage. During the first two stages, the students were asked to think out loud in Korean. The results show that in the composing stage the high level students tended to focus on grammatical forms while the low level groups more concentrated on lexical items. When reformulations were provided, the students well noticed the diffe rences between their original texts and the reformulated ones but a majority of their noticing remained simple noticing without a proper reason or ended up with wrong inferences. Thi s overall shallow and incorrect process at the comparing stage resulted in re latively little changes in the revising stage. These fi ndings suggest that not only the quantity but also the quality of noticing is important for acquisition and more guidance and he lp should be provided for low level learners to benefit from writing and feedback.