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A key element of the technology they used is that the work was automatically marked when you clicked the 'Mark' button, so you get immediate feedback with a tick or a cross. It is very rewarding to sit down, work through something, hit mark and see a load of green ticks. But equally, it is disheartening when they're all red, and of course, you don't get any marks for working. However, you can go back and try to work it through again, and in the exercises, you can click to show the correct answers. They also published worked versions of the questions the following week.
I'm pleased to say that I passed the course in the end, so this has been a useful refresher of elements of my degree in microelectronics from the Newcastle University, but also a very interesting experiment in online learning. I look forward to the next course being announced.
Further information at http://www.mitx.mit.edu/
Update: Some statistics from MITx: 6.002x had 154,763 registrants. Of these, 69,221 people looked at the first problem set, and 26,349 earned at least one point on it. 13,569 people looked at the midterm while it was still open, 10,547 people got at least one point on the midterm, and 9,318 people got a passing score on the midterm. 10,262 people looked at the final exam while it was still open, 8,240 people got at least one point on the final exam, and 5,800 people got a passing score on the final exam. Finally, after completing 14 weeks of study, 7,157 people have earned the first certificate awarded by MITx, proving that they successfully completed 6.002x.