I have a GridView with a header and some rows and want to add another row just below the header using jQuery.

<form id="form1" runat="server">
<div>

    <asp:GridView ID="GridView1" ShowHeader="true" runat="server">
        <Columns>
            <asp:TemplateField HeaderText="Activity Name">
                <ItemTemplate>
                    <asp:Label runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "Name") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>

        </Columns>

    </asp:GridView>

    <asp:Button Text="Add Activity" runat="server" OnClientClick="addActivity(); return false;" />

</div>
</form>

My tries were

$('#GridView1 tbody').prepend('<tr><td>new activity</td></tr>');

Puts a new row above the header

$('#GridView1 table tr:first').after('<tr><td>new activity</td></tr>'); 

Does nothing (at least nothing visible, as well with any other tr element)