Changes in Texas State funding of DFW area school districts

On 12-26-14 the Dallas Morning News published an article titled: "Texas Legislature unlikely to boost school funds in upcoming session."   That article included the per-pupil funding levels for many of the school districts surrounding the DFW area.   That data, in the first three columns below, was taken and several calculations done that lead to some critical questions:

 

The last column in the above chart shows the changes in per-pupil allocation from the state of Texas for each district listed.  Why did these changes happen?   More specifically, why did the average DFW district listed come out with $32 less per student in state funding that the rest of Texas during these years?  Why did Dallas ISD, with such high levels of poverty, come out with $334 less in funding per student?

Here is a 2013 document that should answer this question: http://www.tea.texas.gov/WorkArea/DownloadAsset.aspx?id=2147511834
It not simple.   I am working to understand it due to these unusual changes in funding that happened in the DFW area.