The authors stand by this prediction: Within five years "every" child in "every" grade in "every" K-12 classroom in America will be using a mobile learning device (MLD), 24/7. And a corollary already being seen in MLD-using classrooms: Student achievement will increase "significantly", since time-on-task increases "significantly" when students use MLDs such as smartphones inside the classroom for curricular purposes. Furthermore, the authors present provocative evidence from classrooms in Singapore to New Jersey that Kozma is right and Clark is wrong: The medium--the MLDs--do matter very much in learning! (Contains 1 table and 4 figures.)