Instead of using publisher-created "grammar" exercises with my students, I collect items I find in print in ads, newsletters, signs, etc., and have students identify the errors in the items and suggest corrections.
Such "found" exercises are much more realistic than the ones publishers create. Unlike the grammar exercises, the real-world examples often have more than one error, just as students’ own writing often does.
Also, a found example doesn’t come with directions telling students what type of error to look for any more than students’ own writing does.
And since I give credit (or, if you prefer, assign blame) to the sources, students readily understand how written errors negatively affect public perception of the writers.
The found items make great informal writing prompts because they are short, often funny, and always unpredictable.
The highlight box below gives an example of a 2-minute informal writing prompt using found materials.
Here’s a sentence I plucked from the package of a ream of paper:
The perfect everyday multipurpose paper guaranteed for any printer, copier, and fax machines.
Repair that sentence. Then explain, preferably using appropriate ELA terminology, what the errors were that you corrected.