AITA for refusing to send my son's report card to his grandparents after we'd always shared it?

My fourteen-year-old son put the report card on the table and said, "Please don't send Grandma the whole thing."

I'd sent his previous reports to my parents. Grandma likes keeping family milestones, but she also reads the grades aloud at Sunday lunch and asks how they compare with his cousins' grades.

This report was more mixed than the last one. My son said he didn't want another meal spent explaining each subject. I told him I'd keep it between us and talk to him about it at home.

When Mum asked for the photo, I said we weren't sharing the report this time. She said I had been happy to share when the grades were higher. That's true. I had even joined in the comparison at the last lunch, and I hadn't asked my son whether he wanted his report discussed.

I told her I didn't want the cousins ranked around the table. She said she was celebrating their effort, not ranking them, and that withholding this report would make its contents seem worse.

Now she wants a summary instead. My son doesn't want that either. I want to respect his request, but I also need to own that I helped create the tradition I'm suddenly challenging. AITA for stopping it now?