One of the prime strategies in business today is to outsource work wherever possible. Many employers, particularly small ones, don’t have enough work to warrant a full-time job. But they may parcel that works out to virtual assistants. You can become a VA with just about any type of skill. Administrative skills are most in demand, and usually involving working on very specific projects. Many times, those projects will be assigned because the business owner either lacks the time or the skills to perform them.
Freshman seminar classes (like Statistics 101, for example) can have as many as 500 students enrolled. That's a lot of tests to grade, so professors often employ students within the department to grade tests. Although it's grunt work, the workload is generally spread out based on when the tests are, leaving lots of time in between for academics and extracurricular interests.
A word of caution: Remember that where very little is required, very little is offered. These jobs don’t pay much, and they are not going to provide a reference for your resume. It may take working at several different of these online jobs to pull in the income you want. And as always, know the signs of a work-at-home scam as you sort through the opportunities.