I had my own personal experience with this today!
DD7 is in 3rd, where she's expected to be able to fill a 10x10 grid of random single-digit addition problems in 10 minutes, with zero or one error.
On the first practice test they did in class today, she filled 58 blanks and answered 56 correctly. Oh, and she felt the need to "check her work" by peeking at her tablemate's sheet. (And she had a screaming meltdown at pickup after school, complete with a thrown lunchbox.)
So I made up some practice sheets. She really is weak on speedy recall of her math facts, so I wanted to separate "can get the answer quickly" from "can complete 100 problems in 10 minutes." So we started with a "don't think, just read the problem and write the answer" grid that started with 0+0 and went to 9+9, with each answer being one greater than the one to the left, and one greater than the one above.
It took her 11 minutes just to fill it out. And that was with multiple prompts to get back on track when she'd start looking around. And this was on a full belly, after plenty of physical activity and an extended break from mental work. The math quizzes at school are at 2pm, an hour after the end of lunch and 5 hours into the school day.
