Success or failure in math classes continues to be a risk factor for social exclusion today. Moreover, mathematical skills may also become a key indicator of intellectual disability for some children. However, having access to mathematics can and should be an opportunity for every child of human flourishing, enhancing their understanding, awareness, relationship with their environment, self-expression, and linguistic competency. My eight-year-long study of children with Trisomy 21 aged from 3 to 15, shows that expanding the horizon beyond numeracy and providing living experiences of form, measure, and number that included play, challenge, paradox, mimesis, and beauty is a prerequisite for unleashing the educational power of mathematics. Édouard Séguin (1812–1880) created tables to teach the numeration system to children with cognitive disabilities. Moreover, his educational path towards awakening consciousness (based on the dichotomy me/not me and involving will, action, and intelligence) included geometrical exercises in 3D (using wooden instructional aids designed by him) and 2D (linear drawing). In the present paper, I discuss how Séguin's exercises—which he also intended to be propaedeutic to reading and numeracy—step-by-step inspired the creation of activities that were connected in a learning path to introduce mathematics to children with Trisomy 21.