One of my favorite activities this past year was my weekly math groups. I was lucky enough to have a co-teacher which meant we each had half the class during our Friday groups. The students ask all week to be in the groups. If there is a Friday where we have the day off, we had to make up the day.
With my group, I followed a very set program for my students. The Friday group was a back-to-basic routine. Therefore, I started my group in addition. I let the students move at their own pace. I have binders with all the sheets I need. For example, in the addition group, I start with 2 digit no regrouping followed by 2 digit with regrouping. It progresses from there. I tried to have multiple sheets for each level. If a child seems to get it, I move them ahead a bit. When the child seems to master addition, I give them an assessment. If they pass the assessment, I move them into subtraction. I have a binder for this too which has a similar format.
I would let the students work together on these. Even though students were on different sheets, they were able to teach/learn from each other. Anyone having difficulty with something in particular would work with me in an even smaller group.
When students finish their "work" for the day, they get a coloring sheet that practices the basic facts. It was a fun way to get students to learn their facts.