This convergent parallel mixed methods exploratory study used qualitative and quantitative data collected simultaneously, analyzed separately, and merged for an overarching interpretation. Kindergarten students (n = 27) were randomly assigned to either a control condition of Writer's Workshop or an experimental condition that featured collaboration, student choice, structured self-regulated strategy instruction, and mindset training embedded in the Writer's Workshop framework. The instruction lasted for 30 hours across 10 weeks. Results indicated significant growth for both basic (d = 0.72) and conceptual writing (d = 1.77). Students in the experimental group (n = 14) significantly increased motivation and perseverance for difficult writing tasks. Qualitative data including writing samples, interviews, and recordings supported the quantitative findings. Results indicate that adding mindset and self-regulation strategy instruction to the Writer's Workshop framework may improve motivation and independence in young writers.