The Measures for Early Success Initiative, led by MDRC, aims to reimagine the landscape of early learning assessments for the millions of three- to five-year-olds enrolled in pre-K, so that more equitable data can be applied to meaningfully support and strengthen early learning experiences for all young children. This User-Informed Principles document outlines design parameters for child assessment solutions that meet outstanding needs in the field of early childhood education. The User-Informed Principles intend to spur critical investments and innovations in the existing pre-K assessment landscape by identifying measurement items and solutions, gaps in existing solutions, priority areas for product development, and features of culturally responsive assessment solutions. They reflect what research and best practices suggest are needed.