Why can't I find my label control within my gridview control?

I can't find my label control within my grid like I've seen done in code before, so maybe i'm missing something. In the included code snippets, I first include my markup (HTML) for my grid, then the C# code behind that I've placed in my gridview control's OnRowDataBound method. For some reason my controls aren't being found within my gridview control and i'm not sure why. Any help or code snippets or links would be appreciated. Thanks

markup (HTML)
----------------------------------------------------------
    <asp:UpdatePanel runat="server" ID="upStudentLoginGrid" UpdateMode="Conditional">
        <ContentTemplate>
            <asp:GridView ID="gdvStudentsSignedIn" runat="server" AutoGenerateColumns="false"
                CssClass="SignedInGrid" GridLines="None" AllowSorting="true" AllowPaging="true"
                PageSize="20" PageIndex="0" PagerStyle-HorizontalAlign="Center" OnRowDataBound="gdvStudentsSignedIn_OnRowDataBound">
                <Columns>
                    <asp:TemplateField HeaderText="StudentName" SortExpression="2" ItemStyle-CssClass="StudentName">
                        <ItemTemplate>
                            <h2>
                                <asp:Label ID="lblStudentName" runat="server" CssClass="StudentNameLabel" Text='<%# Eval("AthleteName") %>'></asp:Label><h2>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Week Total" SortExpression="1">
                        <ItemTemplate>
                            <h2>
                                <asp:Label ID="lblWeekTotal" runat="server" Text='<%# Eval("WeekTotal") %>'></asp:Label></h2>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Semester Total" SortExpression="1">
                        <ItemTemplate>
                            <h2>
                                <asp:Label ID="lblSemesterTotal" runat="server" Text='<%# Eval("SemesterTime") %>'></asp:Label></h2>
                        </ItemTemplate>
                    </asp:TemplateField>
.
.
.


C# (code behind)
-------------------------------------------------------------

    protected void gdvStudentsSignedIn_OnRowDataBound(object sender, GridViewRowEventArgs e)
    {
        Label lblSemesterTotal = ((Label)e.Row.FindControl("lblSemesterTotal"));
        Label lblWeekTotal = ((Label)e.Row.FindControl("lblWeekTotal"));

        if (ddlReports.SelectedIndex == 1)
        {
            //HERE I GET A NULL REF. EXCEPTION SINCE THE
            //CONTROL WAS NEVER ORIGINALLY FOUND EVEN THOUGH
            //ITS CLEARLY IN MY MARKUP

            lblSemesterTotal.Visible = true; //<--NULL REF EXCEPTION
            lblWeekTotal.Visible = false;
        }
        else
        {
            lblSemesterTotal.Visible = false;
            lblWeekTotal.Visible = true;
        }
    }

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