Recommended iPad apps for preschoolers and younger students:

Blob Chorus; Rhythm Swing; Music for Little Mozarts; Jam That Jelly; Tune Train;Music Learning Lab; Treble/Bass Cat; Easy Music;The Most Addicting Sheep Game (it is addicting...)     (My First Classical Music Book)

Recommended apps for students improving their reading on the staff:

NoteRush is for Android and iPad/iPhone.  I highly recommend it and may be using it in studio.  At the moment of writing this (August 2016) it costs $5.99 and is well worth the cost.  Much  fun than flashcards for students needing to improve their speed at connecting on page/staff recognition of notes with their place on the keyboard.  It's available in the App store.

Note Works:  a nice little kid centered App available for both on Android and Apple products.   Each game can be individualized using treble, bass, tenor, alto or grand staffs.  It is by DoReMiWorld and the scores can be synced across devices I believe.

Flash Note Derby:  

Note Quest:

Musiclock is currently only for iPad/iPhone devices.  It is a fun little app which allows you to easily play along to a backing track to improvise using scales.  It's easy to adjust the settings and can be used while "jamming" with piano, guitar, voice, another other C instrument, or other instruments once you know the transposition interval.  It's only $11.99 in the App store currently (May 2022).    

This one is a lovely tool that allows you to take a backing track, (for example from the CD that came with your Lesson Book), and turn the dial to change the speed to one you are happy with... Isn't technology lovely.  There are a few different ones out there now but I like this one the best so far.

This is the link to a page of theory information, tutorials, etc.    It is a great site for helping get more information on the theory of music, if you are a person who likes more when it comes to information.