I often had different activities for my lower kids or higher kids. Remember that this was the first year that I even tried some sort of math "centre" system and I had nothing really to base my thinking on.
As the year went on I did start to differentiate some of the activities. One of the activities in my Forest Animal Unit was on ordering numbers from 1 to 20. Now we have worked on this activity many times before in different units so the children were used to the concept. Some children were still working on the numbers 1 to 5 while others were working on 1 to 10 and my highest students were working on 1 to 20. With cards with the numbers 1 to 20 all in the box, it was easy to give the children the numbers they were working on. The only way I think I could make it better would be to put the cards in separate baggies with their names on it so that they could access the activity more easily without adult intervention.
You can see my post on Adapted Measuring to see how I adapted my measuring activities for my physically challenged students.
Check out more links for Math Work Stations Chapters 1 and 2 at Mrs. Wills Blog