INSERT, SCOPE_IDENTITY, And Parameters...

I have a simple table Person (PersonID, PersonName, and PersonAge). PersonID is the primary key and it's also an identity field. Let me paste a sample code and I'll explain at the bottom what's happening. SqlConnection conn = new SqlConnection(@"Server=.SQLEXPRESS;Initial Catalog=Test;Trusted_Connection=True");
conn.Open();
try
{
SqlCommand cmd = new SqlCommand();
cmd.Connection = conn;

// delete all rows
cmd.CommandText = "DELETE FROM Person";
cmd.ExecuteNonQuery();

Response.Write("start... <br><br>");

// ad-hoc insert
cmd.CommandText = "SET IDENTITY_INSERT Person ON";
cmd.ExecuteNonQuery();
cmd.CommandText = "INSERT INTO Person(PersonID, PersonName, PersonAge) VALUES (5, 'John Smith', 20)";
cmd.ExecuteNonQuery();
cmd.CommandText = "SELECT SCOPE_IDENTITY()";
Response.Write("ID = ");
Response.Write(cmd.ExecuteScalar());
Response.Write("<br>");
cmd.CommandText = "SET IDENTITY_INSERT Person OFF";
cmd.ExecuteNonQuery();

// parameter insert
cmd.CommandText = "SET IDENTITY_INSERT Person ON";
cmd.ExecuteNonQuery();
cmd.CommandText = "INSERT INTO Person(PersonID, PersonName, PersonAge) VALUES (@PersonID, @PersonName, @PersonAge)";
p = new SqlParameter("@PersonID", 11);
p.Direction = ParameterDirection.Input;
cmd.Parameters.Add(p);
p = new SqlParameter("@PersonName", "Jon Doe2");
p.Direction = ParameterDirection.Input;
cmd.Parameters.Add(p);
p = new SqlParameter("@PersonAge", 21);
p.Direction = ParameterDirection.Input;
cmd.Parameters.Add(p);
cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
cmd.CommandText = "SELECT SCOPE_IDENTITY()";
Response.Write("ID = ");
Response.Write(cmd.ExecuteScalar());
Response.Write("<br>");
cmd.CommandText = "SET IDENTITY_INSERT Person OFF";
cmd.ExecuteNonQuery();

Response.Write("<br>end.");

}
finally
{
conn.Close();
}

I'm basically trying to insert rows in the table in two ways: one is ad-hoc (hardcoded sql statement) and another using parameters. Using the ad-hoc method everything is OK. Whenever I use the "parameter insert" method I can not get back the ID using SCOPE_IDENTITY (I always get back a DbNull value, the data gets into the table just fine). I'm rather new to using parameters, so it's gotta be something very easy that I'm missing...

Thank you.