Sue Shellenbarger:

It’s a nightly dilemma in many households: A student hits a wall doing homework, and parents are too tired, too busy–or too mystified–to help.
Ordering up a tutor is becoming as easy for kids as grabbing a late-night snack. Amid rapid growth in companies offering online, on-demand tutoring, students can use a credit card to connect, sometimes in less than a minute, with a live tutor. Such 24/7, no-appointment-needed services can be especially helpful to students with tight budgets or tight time frames or those in remote areas.
“All of a sudden, the world opens up to them,” says Michael Horn, executive director of education for the Clayton Christensen Institute, a San Mateo, Calif., education and health-care think tank.
That said, the quality of on-demand scholastic support can be uneven, and the catch-as-catch-can approach to enlisting a tutor may not be best for struggling students who need sustained help. Sessions can bog down on technical glitches, and language barriers can cause problems on sites that rely on tutors from abroad.