I have looked at many different apps but this one has a lot of options I love. It does cost a little bit but it is updated often and improves each time.
First feature, you can have your students log in and it tracks their highest scores.
I believe they have capacity for a least 20 students or more now. My students like finding their own name.
This feature lists their highest scores and give me a look at what we have done before. This is a list of keys they have drilled..
Second feature; the screen has more than one note at a time. This strengthens intervalic note reading. You can adjust how many lines of music they do.
Third feature; you have choices of helps to give even your youngest student a chance to read notes.
A blue dot can tutor them for awhile. Did you notice that you can change the keyboard size. This helps kids who don't use a touch screen much. It keeps them from leaning on other keys.
Fourth feature; You decide what notes to drill. You can do a small range of notes or the whole staff.
You can do only notes of a certain key. This allows older students to review scales and includes sharps and flats.
In review, I-Pad is a thumbs up in my studio and Note Goal Pro is usually on the screen during some part of the lesson,