Did they do this on purpose? Obviously not! So why did I expect those goals on the IEP to be met if they didn't have or had lost the underlying foundation to meeting the goals. If you can't hold you head up, you are not going to look up. If you can't hold your head up, you are not going to follow your speaker with your eyes. If your back muscles and stomach muscles are weak, you are not going to sit up and have the posture for good handwriting. But most of all, when you ask these students to work, they simply don't have the stamina nor endurance.
So what is the poor teacher to do? Continue to demand from slumped over kids. Kids who are anxious. Kids who are whining. Kids who are yawning. Or you can get up and move it, move it. Then at 11:30 when you work on writing you get .... legible signatures, focus, and progress!