Across Texas, credit-recovery courses — self-paced online makeups offered to any student who fails — are expanding rapidly. In the spring and summer, 6,127 students in the Houston Independent School District earned nearly 10,000 credits in such courses, and another 2,500 are taking them this fall. Austin ISD and Dallas ISD enrolled about 4,000 students last year. For districts, they're a cost-effective way to bolster graduation rates, but questions remain over whether the digital curriculum offers the same quality of education as traditional courses. Little research exists on how much, or how little, learning is actually going on.