An independent report has found that an ambitious $1.3 billion program to provide an iPad or other device to every Los Angeles public school student has been slowed by technical challenges, with curriculum that was supposed to be built into the technology often incomplete. The Los Angeles Unified School District launched the country’s largest technology rollout of its kind in 2013 by vowing to equip each of its roughly 650,000 students with an iPad by the end of this year.