My 8th grade son (educational autism IEP) receives an accommodation for extended time on assignments, but according to new language in his IEP, assignments must be turned in by the end of the unit. My son's social studies teacher makes large project assignments due on the last day of the unit. As a result, my son does not receive any extended time on the assignments, even though these large project assignments are the exact type of assignments that my son struggles with due to executive functioning issues. This has been leading to stress and meltdowns at home. I sent a request to the case manager that the "end of the unit" language be deleted or modified to within one week of the end of the unit. She responded that some of my son's teachers were opposed to this request. Any ideas for what I can do next?

I'd recommend asking for a short IEP team meeting addressing this concern so you can talk with all the teachers, explain your concerns, hear theirs, and see what could be done. If not all those teachers would be required to attend the IEP meeting, maybe ask to speak with each teacher individually so you can better understand their position, and see how you could create something that would work for all the staff and your child. If the staff and you can come to an agreement without an IEP meeting, you could always do a no-meet IEP amendment. 

Totally agree with Jenna's approach.  But I'm also curious how the "new language in his IEP" come about??

How is this an accommodation of "extra time" if your child has the same due date as their nondisabled classmates?  If the teachers are not willing to give extra time on the back end, they can provide it on the front end.  They can pre-teach the lesson to your child 3-5 days before they teach it to the class and give them the assignment 3-5 days before the rest of the class gets it.  This way your child gets a jump start on the assignment which gives them more time than their classmates even though they all have the same due date.  The Social Studies teacher could have the rest of the class have a due date that's 3-4 days before they end the unit and then let your child hand their assignment in the last day of the unit.

There are ways to provide your child with the extra time they had in the past that helped them to be successful and still not hand in work after the end of the unit.  You just need to think out of the box.

I also think you need to speak with the teachers to understand their restriction of the extra time accommodation.  It's possible they think having to finish the old unit is too much of a distraction with keeping up with the new unit.  If they do 3 units per marking period, you don't want the 1st unit's work finished 3-4 day after where the 2nd unit's work ends up 6-8 days after the unit ends.  (Do they know your child's track record where farther into the marking period the lateness doesn't get progressive?  They might be judging him based on a student they had in the past who was like this.)  It's possible they don't understand the disability and why it's key for your child to be given real extra time where they have time to melt down, get anxious,  perseverate where they make no progress and get through the assignment eventually.  When you know their backstory, you'll be better prepared to explain why your child needs the past wording.