In Motion:
Start a new Title project and delete the default Text (it's just easier than going through all the steps to "normalize" it.)
Whether you use a Title Background or not for the Title template is up to you, but have Motion create a Title Background (it can be "hidden" if you don't want it).
Create a New Group.
Add a Text Object and center it up - and Center the text. It can have mulitple lines or not... you'll see why in a minute.
Add a Behaviors > Basic Motion > Align To and duplicate it.
To Align To (bottom-most), add the Title Background to the Object drop well and do the same for the other Align To.
For the bottom-most Align To, set Align "text" to Text Ascender > Center.
Set the To "Title Background" to Bottom.
For the upper Align To, set the Align "text" to Text Descender > Center.
Set the To "Title Background" to Top.
For the upper Align To, set the Transition to Custom.
Publish the Custom Amount which can be keyframed from 0-100% and anything in between.
For the first half of your animation - keyframe 0 - 50% (for "dead center") then the second half up to 100%. [Dead center will depend on Ascent and Descent of the font(s) used — and you can simply adjust it be the percentage keyframe.]
NOTES:
Fonts are *** all different *** ascents and descents. These are extremely variable depending on the Font creator/artist. No two are likely to be exactly the same. Therefore, there will be some fonts where the characters are drawn outside of these limits!!
I recommend also publishing the Offset > Y parameters of both Align To behaviors so that you can compensate if necessary so that you can force the text to start and and completely offscreen AND you can customize where "dead center" occurs (if that makes any sense.)
To hide/remove the Title Background, place it in its own group at the bottom of the Layers List. Uncheck the Group visibility. The Title Background is used for the Align To's because it should always be the appropriate height for any project settings.
HTH