Dot for Time
I can't remember who told me this, but they were a genius.
"A child's concentration span is their age plus a minute."
It is accurate and entirely useful, and I use it all the time in my planning of activities. As a (mainly) year three teacher, I budget eight minutes per task. A longer task might be 16 minutes, with a refocus in the middle.
One things that has been working brilliantly for me recently, and may well help the children (more importantly) is to dot for time. This is probably very old fashioned and unoriginal, but if they are writing a passage of text, if I dot where they are currently at with a pen, then tell them I will see how much they have done in eight minutes time, their actual workrate and quality of work improves.
I was expecting it to decrease their handwriting standard, but it really doesn't appear to!