Apple Motion 3 - Manual (Page 655)

Chapter 7 Using Text 655
Important: Before any animation can occur, you must explicitly add at least one
parameter to the behavior from within the Inspector. Until a parameter is added,
adjustments made in the HUD have no effect.
2 With the Sequence Text behavior selected, display the Behaviors tab in the Inspector.
The upper area of the Sequence Text controls contains the Add and Remove pop-up
menus, which are used to select parameters to add to the behavior, or to remove
parameters. The second group of parameters are the Sequence controls, which include
options for setting the direction of the animation, whether the animation is applied per
character, per word, or per text layer, and so on.
3 In the Parameter row, click the Add pop-up menu, choose Format, then choose Scale.
The Scale parameter is added to the behavior and is set to 100% by default (which
represents the original size of the text).
Sequence controls
Add or Remove parameters