Accessing Controls From Separate Classes

I have an ASP.NET Web Site I am creating in Visual Web Developer 2008 Express using Visual Basic as the language. It is actually a rewrite-with-mods of an existing ASP script and I'm trying to chew what I've bitten off. I created my page with a text box (txtOutput) on it and since the end product is very complex, and it's generally good practice to separate like functions, I have created 4 separate classes in the App_Code section.

My main page is Sync.aspx and has a code file Sync.aspx.vb with it.

One of my code files is SyncDatabases.vb and in it I have created

Public Class SyncDB

In that class I have created some routines such as

Public Function ReadMSDB(ByVal SQLString as string) as Boolean

In this routine I want to put information in my text box txtOutput on the main form (the default - Form1).

My problem is that if I try:

Form1.txtOutput.Text = "Hello world"

or just

txtOutput.Text = "Hello world"

it says Name 'Form1' (or 'txtOutput') is not declared. I am sure I am missing something simple but have no clue what it is. I assume it's the fact that the write command is in a file (class?) outside the file (class?) containing the page itself but I don't know how to address it properly.