The present study examines the potential effect of scaffolding instruction on Jordanian EFL tenth-grade students’ overall writing performance and their performance on the sub-skills of focus, development, organization, conventions and word choice. The study follows a quasi-experimental experimental/control group, pre-/post test design. In the experimental group, 20 female tenth-grade students from the North-Eastern Badia Directorate of Education (Jordan) were taught to generate ideas, structure, draft, and edit their essays using agency scaffolding and the scaffolding principles of contextual support, continuity, intersubjectivity, flow, contingency and handover, within the Zone of Proximal Development. Another group of 28 students was instructed conventionally per the guidelines outlined in the Teacher’s Book. After the treatment, descriptive statistics and ANCOVA were used to analyze the students’ scores on the pre-test and the post test. The results showed that the scaffolding instruction group outperformed the control group (at a≤ 0.05) in their overall writing performance and in their performance on all writing sub-skills except the sub-skill of development.