EF is much more than organization; Organization is just one of eight key skills listed as being involved in executive function.

This is what seemed to match, between your description and the EF article:
Originally Posted by tillamook
two big stressful assignments have derailed him...
1) act up and withdraw during class time...
2) increasingly angry...
3) "back against the wall" fear reaction. Get me out of here...
4) teachers called him on his recent behaviour... He was surprised and upset...
5) things are overwhelming...
6) Refusal to talk, refusal to go, refusal to discuss going in a different direction...
7) Also, this is a kid who has difficulty making decisions.
In the list below, the numbers are added to correspond to the poster's list, above.
Originally Posted by excerpts from EF issues, Understood.org[/i
]Having issues with executive functioning makes it difficult to:
- Keep track of time
6- Make plans
- Make sure work is finished on time
- Multitask
- Apply previously learned information to solve problems
- Analyze ideas
6- Look for help or more information when it is needed
...
Executive functioning issues can produce a wide range of symptoms. Depending on which skills your child struggles with the most, and the particular task she’s doing, you might see the following signs:
- Finds it hard to figure out how to get started on a task
- Can focus on small details or the overall picture, but not both at the same time
- Has trouble figuring out how much time a task requires
- Does things either quickly and messily or slowly and incompletely
4- Finds it hard to incorporate feedback into work or an activity
- Sticks with a plan, even when it’s clear that the plan isn’t working
- Has trouble paying attention and is easily distracted
- Loses a train of thought when interrupted
- Needs to be told the directions many times
7- Has trouble making decisions
- Has a tough time switching gears from one activity to another
6- Doesn’t always have the words to explain something in detail
- Needs help processing what something feels/sounds/looks like
- Isn’t able to think about or do more than one thing at a time
- Remembers information better using cues, abbreviations or acronyms
...
There are several key skills involved in executive function. But your child may not struggle with all of them to the same degree. Executive skills include:
1- [i]Impulse control: This is your child’s ability to stop and think before acting. Impulsivity can be a symptom of ADHD. Kids who have trouble with impulse control may blurt things out. They may do unsafe things without thinking it through. They’re likely to rush through homework without checking it. They also may quit a chore halfway through to go hang out with friends and have trouble following rules consistently.
2,3,5- Emotional control:This is your child’s ability to manage her feelings by focusing on the end result or goal. Emotional control and impulse control are closely related. Kids who struggle with emotional control often have trouble accepting negative feedback. They also may overreact to little injustices. They may struggle to finish a task when something upsets them.
6- Flexibility: This is your child’s ability to roll with the punches and come up with new approaches when a plan fails. Kids who are inflexible think in very concrete ways. They don’t see other options or solutions. They find it difficult to change course. They may get panicky and frustrated when they’re asked to do so.
- Working Memory...
4- Self-Monitoring...
6- Planning and prioritizing...
6- Task Initiation...
- Organization...
What, specifically, was stressful about the two assignments? While many individuals may not enjoy public speaking or presentations, most do not shut down or become derailed. I'd look for an underlying cause. If not EF, then in what direction to search...?