The Wikispaces team has announced the news that they are closing up shop for good. On their Classroom and Free Wikis page they note that:
we do not have a way of exporting your Wiki direct from Wikispaces to another site
What that means is that Wikispaces sites will be stuck soon with no option.
We at CiviHosting, however, have developed an migration tool to allow users to convert their sites to another Wiki format. See our Wikispaces Migration page for full details.
I have used wikispaces as a teacher for about 8 years and would welcome this option!