Response.Redirect is not clearing form. Why?

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ASP.NET

I have a form that a user can fill out. When the user clicks the submit button the form pops up a success message and redirects back to the same form but the data is not cleared out. What did I do wrong?

protected void Submit_Click(object sender, EventArgs e)
       {

           SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["HotConnectionString"].ConnectionString);
           con.Open();

           SqlCommand cmd = new SqlCommand("Insert into Table2013 (INST_ID, UNITID, ASTUDENTS, ACOMPLETED, ATRANSFERS, BSTUDENTS, BCOMPLETED, BTRANSFERS, YEAR, DATE) values (@INST_ID, @UNITID, @ASTUDENTS, @ACOMPLETED, @ATRANSFERS, @BSTUDENTS, @BCOMPLETED, @BTRANSFERS, @YEAR, @DATE)Insert into Table2014 (INST_ID, UNITID, ASTUDENTS, ACOMPLETED, ATRANSFERS, BSTUDENTS, BCOMPLETED, BTRANSFERS, YEAR, DATE) values (@INST_ID, @UNITID, @ASTUDENTS, @ACOMPLETED, @ATRANSFERS, @BSTUDENTS, @BCOMPLETED, @BTRANSFERS, @YEAR, @DATE)", con);

           cmd.Parameters.AddWithValue("@ASTUDENTS", TextBoxTNUGSC.Text);
           cmd.Parameters.AddWithValue("@ACOMPLETED", TextBoxTNUGSCD.Text);
           cmd.Parameters.AddWithValue("@ATRANSFERS", TextBoxTTOUG.Text);
           cmd.Parameters.AddWithValue("@BSTUDENTS", TextBoxTNGSC.Text);
           cmd.Parameters.AddWithValue("@BCOMPLETED", TextBoxTNGSCD.Text);
           cmd.Parameters.AddWithValue("@BTRANSFERS", TextBoxTTOG.Text);
           cmd.Parameters.AddWithValue("@YEAR", TextBoxYEAR.Text);
           cmd.Parameters.AddWithValue("@DATE", TextBoxDATE.Text);
           cmd.Parameters.AddWithValue("@UNITID", TextBoxUNITID.Text);
           cmd.Parameters.AddWithValue("@INST_ID", TextBoxINST_ID.Text);

           cmd.ExecuteNonQuery();
           con.Close();

           if (Page.IsValid)
           {
               ScriptManager.RegisterStartupScript(this, this.GetType(), "script", "alert('You Have Successfully Submitted the Cohort');", true);
           }
           else
           {
               Response.Redirect("Gradrate.aspx");
           }


       }