Yes, I gave a lesson in test answer bubble filling to my ten year old last week.
I decided to have my sons take the Iowa test in May. They've never taken an official, recorded standardized test before.
My younger son tried to take shortcuts on the bubble filling, doing a sloppy job. I explained if they're not filled in correctly he gets the question marked wrong. He then asked if he could mark two answers per question, and I had to answer, "No, then you get that one wrong too."
I am annoyed to find subjective questions in these test prep books. Some questions are written by older people about things that are not common in children's lives today. Life in America changes. Kids today may not use the same language or experience the same things. What was common in the life of the test-question writer may be something today's kid has never seen before.
Some of the questions for math do stupid things with the numbers that are never use in real life nor are ever done in math schoolwork.
I have found some errors as well. Sometimes there are two right answers and what makes one right and one wrong is a mystery to me!
The test prep process is frustrating. I resent that today's kids are being ranked and rated by such subjective or unclear test questions. I now see how the test results can be inaccurate!