How do I reach them all?

Differentiation. It's one of those education "buzz words" that seems to constantly be floating around. Many of my curriculum and instruction classes focused on differentiation in the classroom. I thought I understood the concept; I thought I had a firm grasp on how to implement differentiation in my classroom.

However, I'm discovering that the real-world application of differentiation is very difficult. We just finished our third six-weeks' assessments with the kids. By this point in the year, I can almost predict what my students will be able to do. The majority of my kids are right where they are supposed to be, but then there are a few that have been struggling since the very beginning and keep falling farther behind. I want to do my best to help these students succeed. But I'm not sure what to do. Maybe I'm just using this as an excuse, but it seems to be extra hard to create differentiation in a Kindergarten classroom. The difficulty is that my students are unable to do much independent work. If I give them directions for an activity, they can only remember one or two directions at a time. They can't read well enough for me to give any kind of directions on paper. So, I have difficulty finding time to work one on one or in small groups with these students that need extra help.

My students that need extra help are especially weak with their numbers. My students are supposed to be able to identify numbers 1-50 at this point. A few of my students still are unable to identify the numbers 1-10. I have some time to review with them during centers, but all the students look foward to centers so much that I hate to pull these kids out during centers and burn them out with extra review.

So, basically I'm at a loss for what to do to help these students have a chance to catch up in time to be ready for first grade. Any suggestions for real-world proven techniques that work in Kindergarten to help students?