You can search (filter) the view in the Scripting Index. This filter shows that the Display Boxes that respond to the << Set Font Size() message is limited:
 

 
A Table Box does not include this message in its protocol. This sample script shows how it works with some of these display boxes:
 
Names Default to Here( 1 );
New Window( "Font Playground",
	Outline Box( "Text All Over the Place",
		tb = Text Box( "Hello, world!" ),
		teb = Text Edit Box( "Hello, world!" ),
		scb = String Col Box( "Message", { "Hello, world!" } ),
	)
);
Wait( 3 );
{ tb, teb, scb } << Set Font Size( 18 );