The confusing apostrophe

In school work JM has been learning about possessives. In particular, he is learning about single possessive and plural possessive. I know it can be confusing as I've run into people online who are confused by it as well. Today JM was studying for his spelling test, which admittedly was full of easy words. Words such as boy's and boys'. He knew the words, but I could see a potential train wreck approaching. I cautioned him to really study where that apostrophe was placed and know why it was placed there as it could be confusing during a spelling test. Being the almost 9 year old that he is, he assured me that he knew where it went.

Since we are now in a portion of schooling where we are expecting JM to take more of the initiative in learning what he needs to learn, and learn to study, we let him "falter" some. This was one of those times. We did not just leave him to study alone, we did some reviewing of it together, we talked about it, but we didn't force him to practice the words over and over and over and over.

He did get confused on the placement of that apostrophe. He did spell the words correctly, but placing that apostrophe got him in the end.

Did he learn a lesson? I have no idea, I hope so. He will be studying the words again, learning about the placement of apostrophes during single possessive and plural possessive...again. He will also take a 2nd spelling test on these words. I am thinking he will do much better on the 2nd test.

One thing is for certain, spelling and grammar are not his strongest subjects.