We are not aware of any federal guidelines that specify a minimum or maximum walking distance for elementary school students. At the state level, the minimum and maximum can vary state to state and even from school district to school district. To determine what the distance for a particular school you will want to contact the school and school district. You may also want to contact your state's Department of Education and speak with their staff that deals with school transportation. They may have a policy that specifics what the distances are for your state or they may leave it up to the individual school districts or schools.