voter pre-registration

In a post about registering high school students to vote, rachelmanija mentioned pre-registration for 16- and 17-year-olds: they fill out the voter registration forms ahead of time, and then can vote once they turn 18. She mentioned that several states other than California have this, so I took a look, and Massachusetts is one of them. At least in Massachusetts, the voter registration process is the same as for people are 18 or older.

For all I know, those of you who have teenage offspring, or spend much time around teenagers, already know this, but it seemed worth mentioning.