Math facts

During the past two weeks I have been implementing my 2nd mini project. I am a bit disappointed that I did not think of it earlier. My students have spent time (10 minutes) daily engaged in math games/activities and seem to enjoy playing them. Then again it is not all about what they enjoy but more so if it is making a difference. From my observation, I think it is as students are talking about math facts through daily practice. I took a brief survey with my students and 15/19 of my students believe that these games are helping them recall their facts more fluently. After giving another written time test at the end of week 2, there were several students who improved their score. However, I had a couple students decrease their score.
Students enjoy playing these games with partners. I have a few struggle in working with others so it is making this activity difficult.
I have seen progress in 2 weeks, so I am wondering what kind of progress can be made in just a month. I also am communicating the activities and games with parents in hopes students continue to work on these activities at home. I have shared written and oral scores with parents and will do so again at the end of the school year.
So far I have a few fluent students with basic facts but have a ways to go with quite a few of my students. Why are some of these facts so difficult for students? Right now, my students should be fluent with doubles, combinations of 10, near doubles, and plus 10 facts. They seem to struggle and take more time with those irregular facts. Hopefully as we continue our practice, students will recall those facts with little or no effort.