If would depend on the school. My kids have access to computers at school and at home, so I don’t think there’s a need. By late middle school or high school a laptop might make more sense, but knowing how amazingly well-equipped the schools here are, I don’t think it’s a necessity.
My daughter is in 6th grade and uses laptops at school. Plus, they have more than one computer lab. Having her own laptop would be redundant. If her school didn’t have enough computers or laptops to go around and the teachers still expected that much work to be done on computers, I might consider it. Probably not for a 4th grader though.
For homework, I guess it depends on your home situation. If sharing a computer isn’t convenient and you can afford a laptop, then go for it. I’d be careful not to call it her laptop though but stress that it is a tool for the family. That way you can set up ground rules like not allowing her to use it alone in her room or take it out of the house.
I’d suggest you ask the teacher or principal. The laptop craze could be parents trying to outdo each other and more of an accessory trend than a needed tool. I’d save my money until I saw a need for using it on something like that. Kids here in 5th and 6th grade commonly have iPhones, which I think is kind of ridiculous. My poor deprived kid doesn’t have any kind of cell phone!