The promise of digital education is still out of reach for most American students. For schools that haven’t yet made technology an integral part of every student’s school day and every teacher’s lesson planning, the problem is often basic: Their Internet connection is too weak and their laptops (if they even have them) are too old to handle whole classrooms of students spending most or even part of their day online. Fewer than 20 percent of teachers say their school’s Internet connection meets their teaching needs, according to the White House.