I need help

I work in a traditional middle school in South Minneapolis. I used to teach 8th grade. I taught Algebra 1 to all the 8th graders.  I worked very hard to be sure all 8th graders were included, regardless of past performance.  It had its ups and downs but generally went okay.  I think some (maybe even many) of my students left me with a deeper appreciation of the beauty of mathematics.

My job has changed.  I am now the "Math Specialist".  My responsibilities are to teach support classes of 8 to 12 students who are struggling.  I teach two sections each of 5th graders, 6th graders, 7th graders, and 8th graders.

I'm the one who is struggling.  One-fourth of the school year has passed and I still have not figured out how to make it work.  Behavior, disenchantment, and a little bit of outright sabotage have been too much for me to overcome.

I know this model of instruction is not a good one - segregating the lowest achievers.  But that's what I'm stuck with for this school year.  Can anyone help me?