Board Thread:Naruto Discussions/@comment-5054236-20150729184811/@comment-24949460-20150810173208

Omojuze wrote: Gaara's sand isn't Magnet Release. And Rasa was taught Magnet Release, by the Third Kazekage, or so I believe (right Seele?) so...

Magnet Release isn't taught it is inherited. Because if it can be taught to anyone then all the Sand Ninja would have possess it and they wouldn't have lost the battle as much against the Leaf Village.

EDIT: This wiki also stated that the Magnet Release is a Bloodline Limit or Kekkei Genkai.