You don't need to sign up, but the school/teacher need to know that your kid is a bus rider, and which bus they should be getting on at dismissal. There is usually a form they have parents fill out for this.

If you can, have him take the bus in the morning a few times so he learns the route and the driver knows him. Then let the school know it'll only be afternoons after that.

Otherwise, if you have before care, let the school know he'll only be riding home and where he should get off.

First grade son new to MCPS - he will take the bus home. Do we need to sign up, tell the school, fill out any forms? I looked at the bus route info and figured out the stop needed but unclear what else to do beyond that...