Hi Rebecca
I'm assuming that by Scaled Output Window you mean a Layout where the Map Window is shown thru a frame.
The text on the grid is shown as labels and so you will have to make the label font bigger. This is probably also what you have done.
I think you might have made the labels bigger in the wrong map window. Be aware that when you have a Map inside a Layout window this is a copy of the original map. Make sure that you change the label settings for the map in the layout, not the original map.
Let me know if I have misunderstood your question or what you are trying to do.