When I was in school we had a similar reading project, but only once, not monthly. We could choose a book from the school library (it was a big deal that we even had one because the school was pretty small) and had to do some small tasks, like summaries of chapters or other things I can´t remember.
It was much more fun than reading books the teacher chose, because everyone had something they were interested in and I think that had an impact.

I think it´s great that you spark the interest to read in your pupils, well done :)