Students can now take the TOEFL every single week. In the past, they could take it only once every two weeks, but ETS has changed this policy. There were rumors of this change last month, and now it is official. You can find the details in the most recent version of the TOEFL Bulletin.
It says: “There is no limit to the number of times you can take the test, but you cannot take it more than once in a 3-day period. If you already have a test appointment, you cannot register for another test date that is within 3 days of your existing appointment. “
Note the the old version of the bulletin referred to a “12-day” period.
I think this is a positive change, however it will still take about two weeks for scores to be reported. This means, of course, that you might register for a sitting that is not actually required.