Ensuring Grade Level standards

In my classroom, we are given an open ability to use whatever curriculum we would like to best fit our students.  As for following and adhering to grade level standards I use the general education grade level standards as a guide.  It doesn't mean we keep on track with them as far as what we cover by when but I do use them to guide my instruction.  Since I have a combined class of grades 2-4 I do a lot of 2nd grade and differentiate for the 3rd and 4th since they are bridging gaps.  I also do the reverse for the 3rd and 4th for the 2nd graders.  Recently we did a whole lesson on learning the states and the capitals since two of my upper graders asked about it.  I differentiated for the lower grades and they all had a fun time learning.  I do the same for math, right now I have everyone in the class learning their multiplication facts.  They are all going to need to and the sooner the better so they won't have to struggle on that hill so hard. 
As I stated I use my gen ed curriculum to help my planning and I try to stick as close as we can with subject matter but use a lot of differentiation to help complete the holes and true understanding of subject matter.