xml collection best practices

i'm formulating an concentration store hierarchical collection equipment an xml record i'm wondering attention customary storing collections xml. following twin formats preferred? (if there another choice i'm seeing, greatfully advise.)

option a

<school>
    <student name="jack" />
    <student name="jill" />
    <class name="english 101" />
    <class name="math 101" />
</school>

option b

<school>
    <students>
        <student name="jack" />
        <student name="jill" />
    </students>
    <classes>
        <class name="english 101" />
        <class name="math 101" />
    </classes>
</school>