Why isnt this working?

I am attempting to make a countdown code that works on a GUI, here is what I have so far.

function countdown(number)
        for i = number, 1, -1 do
                game.Workspace.timer.Value = i 
end   

There is a NumValue called "timer" and this is the code inside the GUI that is being used as a local script.

workspace.timer.Changed:connect(function(v)
    script.Parent.TextLabel.Text = v
end)