As the coronavirus pandemic closes schools, in some cases until September, American children this month met their new English, math, science and homeroom teachers: their iPads and their parents. Classes are going online, if they exist at all. The United States is embarking on a massive, months-long virtual-pedagogy experiment, and it is not likely to end well. Years of research shows that online schooling is ineffective — and that students suffer significant learning losses when they have a long break from school. Now they’re getting both, in a hastily arranged mess. And the kids who suffer most from the “summer...