What is the first thing that the learning science researchers ask when the enthusiastic software developers show us a bright shiny math app they want to deploy in a classroom
"how will using this make a child FEEL?"
Why? Because this is the precondition for everything. And I mean that on a visceral, human level. You build for kids, you ask: how long are you asking a small child to sit in a seat? Look at a screen? Touch and move screen objects with their fingers?