It went on for about two years and the children enjoyed it-they were aged 7 and 8 years. However eventually time couldn't be found during school hours to fit in our bookcrossing club and when we tried it at lunchtime it wasn't very popular at all (!) which is understandable. Most of the children preferred to play. The books I took to the school were spread around the various classrooms when the club was disbanded so no doubt are still being read during wet playtimes and maybe being taken home by the pupils but unfortunately I never get any journal entries now. When the club was in force I mostly used to do the J/E's on the pupils behalf once they had told me their thoughts about what they had read and scored the books out of 10. However one or two of the parents joined in and helped the children to make their own J/E's. Good luck with your project if you manage to get it going.
My last project was only partly successful, because the website was in English only (which was too hard for most of my students, as they already had troubles reading in German). It was a success, because the kids read a lot of the BC books, but they did not journal them (very hard, too). Now I'm trying again - other school, different kids. Let's see! Age is 12 yrs.