We had the packet thing...home on Monday back on Friday in first grade...not 12 pages long.
You might ask the teacher, seeing as he is not used to that workload, if he could try getting packet on Friday instead to give you a few additional days to spread it out. You could agree for him to just get a head start on the tasks like writing the words and hold off on tasks until the week that he hasn't been introduced to (maybe a math concept.)
I know that kids with accommodations or kids in the beginnings of RTI stages were sometimes given extra days on the packets.
As he gets more comfortable with the work load you could try moving it back to Monday like the other kids. Consider asking for 3 or 4 weeks to transition and then see if he can manage the Monday.
I personally liked the packet system because some days he had plenty of time to work and other days he did nothing and whenever he was bored I always said pull out your packet. If he had to ride along to some activity for big brother? Bring your packet! (I kept a pencil box in the car with scissors, colored pencils, pencils, glue, and anything else he needed in the car).
It also taught him how to skip around, plan, manage his time, and we actually got him using a calendar. And sometimes he even had to wake up a bit early on a Friday morning to finish up and he HATES that with a passion so it only happened once or twice.
