The error-correction program "Criterion" provides students with an immediate essay feedback using tools that can analyze and review writing automatically. This feedback covers grammar, usage, mechanics, style, organization, and development. With its diagnostic tools for scoring essays and offering relevant feedback, the error-correction program provides a way to speed up the otherwise time-consuming process of essay composition and evaluation. The usefulness of the error-correction program is highlighted by analyzing the extent to which it helps second language learners improve their writing abilities, with a focus on the degree of student improvement caused by the program's prompts from the first draft to the final essay submission. The purpose of this study is to determine the extent to which second language learners can improve their writing capacities using a specific set of online instruction materials, the error-correction program online essay writing tool in a group of 96 university students at the intermediate level of English.