public class Entity
{
    public Entity()
    {
    }
    public Entity(string c, string f)
    {
      name = c;
      school = f;
    }
    public string name;
    public string school;
}

List<Entity> entityList=null;
XmlSerializer xs = new XmlSerializer(typeof(List<Entity>));

using (StreamReader sr = new StreamReader(configPath))
{
   entityList = xs.Deserialize(sr) as List<Entity>;
}

using (StreamWriter sw = File.CreateText(configPath))
{
  xs.Serialize(sw, entityList);
}

<?xml version="1.0" encoding="utf-8"?>
<ArrayOfEntity xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 <Entity>
  <Name>Alice</Name>
  <School>SJTU</School>
 </Entity>
 <Entity>
  <Name>Cici</Name>
  <School>CSU</School>
 </Entity>
 <Entity>
  <Name>Zero</Name>
  <School>HIT</School>
 </Entity>
</ArrayOfEntity>