ASP.net Show "please wait " message as page loads

Hi

I am currently using the JavaScript further down to put a "Processing..please wait" message up while VB.net code runs (interacting SQL).
This all runs on a button click. How do I do the same for the following Page_Load event. Thanks

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not IsPostBack Then
            Call Load_School_Names()
            Me.btnSaveAdditionalChild.Visible = False
        End If
    End Sub

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    	<style type="text/css">
		.pleaseWait { width: 50%; height: 100px; background-color: #cccccc; display: none; z-index:999; position:absolute; left:25%; top:10%}
	</style>
	<script type="text/javascript" src="http://code.jquery.com/jquery-1.9.1.min.js"></script>
	<script type="text/javascript">
		//<![CDATA[
	    function showLoading() {
	        $('.pleaseWait').show();
	    }
		//]]>
       </script>

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          <div class="pleaseWait">Processing... please wait!</div>
		                     <div>
                        <asp:Button ID="btnSave" runat="server" BackColor="White" Font-Names="Calibri" 
                            ForeColor="#003399" Height="29px" Text="Save" Width="217px" OnClientClick="showLoading();" />
           
                            </div>

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