We examined the differential effects of the social cognitive model of sequential skill acquisition (SCM intervention) and the self-regulated strategy development model (SRSD intervention) for writing. One hundred and twenty-one 5th- and 6th-grade Spanish students with learning disabilities (LD) and/or low achievement (LA) were randomly assigned either to an experimental intervention group or the standard instruction group. Both self-regulatory interventions showed a significant improvement with a large effect size in the structure, coherence, and quality of students' writing products, as determined in terms of reader- and text-based measures. Additionally, both interventions demonstrated a substantial increase in the time students spent on writing and revising their texts; the latter was noted especially in the SCM intervention group although only the SRSD intervention showed a significant increase in the time students dedicated to planning text. Finally, with regard to writing self-efficacy, only the SCM intervention group experienced a significant improvement. (Contains 6 figures and 11 tables.)