Dad scolds mother-in-law for telling school employee that she's her 6-year-old grandson's guardian: 'No. You’re his grandmother. I’m his dad, and this is his mother.'

She's making him look like an absent parent, and he's not. 

Not all parents are guardians, and not all guardians are parents. Every family is different, and it's best practice for schools not to assume that all their students have a mom and a dad who are caring for them at home. There's a reason teachers tell their students to bring permission slips home to "their parent or guardian" rather than just their parent. 

Some teachers want to be even more inclusive, telling kids to give permissions slips to "their grown-up." That could be a little too vague, because who exactly is their "grown-up"? A grandparent could be heavily involved in their grandchild's life without serving as a guardian. They shouldn't give their permission slip to just any grown-up who happens to be in their lives. The role of a guardian is much greater than that of an aunt who occasionally picks them up from school when their mom is busy. She probably shouldn't be the one who signs the test when they fail! She is an important, valuable member of the family, but she is not a guardian. It's essential that she not make decisions that guardians should make, and that she not identify herself as a guardian to her nieces' or nephews' schools. The school needs to know the identities of the adults caring for the children they educate for safety reasons.