We present the evolving fraction conceptions of two elementary school children with mathematics learning disabilities (MLD). We use qualitative analyses to capture the mathematical knowledge and experiences of each child and show how teaching was used to support advancement of their fractional reasoning. Results illustrate two viable pathways of advancing fractional thinking, both of which reflect students' increasing levels of units coordination over time. We argue that recognizing and building on each child's strengths--while respecting and accommodating for their MLD--was central to promoting their learning. Results provide an existence proof of a new evidence base for student-centered, problem-based instruction for students with MLD, grounded in a careful understanding of student mathematical thinking and accommodations for cognitive differences.