For Android, I suggest going to YouTube and watching videos from the Android Bootcamp (by Marakana). I'm relearning Android and I think this is pretty efficient.

For iOS, the Stanford iOS course was pretty decent. iOS may have changed a bit from when I watched those videos. Not sure if they are current anymore.

P.S. I don't recommend the coursera course on Android dev. I started watching it but it seemed to be going super slow.