How do I specify the Linq OrderBy argument dynamically?

Here's a possiblity using reflection...

var param = "Address";    
var propertyInfo = typeof(Student).GetProperty(param);    
var orderByAddress = items.OrderBy(x => propertyInfo.GetValue(x, null));

You can use a little bit of reflection to construct the expression tree as follows (this is an extension method):

public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByProperty,
                          bool desc) 
{
     string command = desc ? "OrderByDescending" : "OrderBy";
     var type = typeof(TEntity);
     var property = type.GetProperty(orderByProperty);
     var parameter = Expression.Parameter(type, "p");
     var propertyAccess = Expression.MakeMemberAccess(parameter, property);
     var orderByExpression = Expression.Lambda(propertyAccess, parameter);
     var resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType },
                                   source.Expression, Expression.Quote(orderByExpression));
     return source.Provider.CreateQuery<TEntity>(resultExpression);
}

orderByProperty is the Property name you want to order by and if pass true as parameter for desc, will sort in descending order; otherwise, will sort in ascending order.

Now you should be able to do existingStudents.OrderBy("City",true); or existingStudents.OrderBy("City",false);