[jschulenklopper]

Interesting idea - and great that so many are helping in contributing exercises.

  To solve the problem, she created a site last year that presents the
  practice problems and prevents students from being able to move on to the
  next ones without submitting a solution to the previous problem.

I think that Project Euler, https://projecteuler.net/, has a better implementation of this. All problems are available, but they become harder and harder (at least in the beginning - they might level out now). That already is a stimulus to solve the problems in the intended order, in addition to the 'level degrees' awarded after solving a batch of problems.

Additionally, the Project Euler forum in which solutions are shared and discussed is only available once you've submitted the correct solution.

OK, back to Euler. I'm close to a next level award...