My class meets once a week for two hours with one hour in a computer laboratory. The last two sessions were used to get students registered and performed a mock session for an online management system and do a trial run on Tumblr. At the same time, they were asked to post a short paragraph about their prior experience with mathematics.
Today they were given a problem to solve and then ask to post their solutions in Tumblr. I commented on their results and give them an opprotunity to correct any mistakes. If on the second try they didn't get the right answer, I suggest that they look at one of the postings for possible hints.
The session went very well, given the fact that they never seen such problem in class. I next step is to have students post at least one response to any student in the class for a weekly online activity. Let's see how it goes!