Hi Selena,
The $99 product is the
Music Curriculum Pack. It is simply the pre-made curriculum (Semester 1 and 2) that you can add to the Little Musician software, and you can play it as is (i.e., without any customization). You won't be able to edit the lessons in it or change any playback setting, though, as your software will be in the "Lite" mode.
The $179 or $189 product is the
Little Musician Basic kit. It comes with the pre-made curriculum and PRO usage of the Little Musician software. The PRO features will let you edit or customize the lessons, and you can also make your own set of lessons if you like.
For both products, you will be able to install the program on UP TO 2 computers. For example you can install Little Musician on your home desktop PC and on a laptop so you can continue the lessons even when you're traveling.
The main difference between the Music Curriculum Pack and Little Musician Basic is the access to full lesson customization features in the software.
If you are not interested in creating or customizing lessons, then you can just go with the Music Curriculum pack. Later on, if you feel your son may benefit more if you customize the lessons or if you make some of your own, you can buy the PRO KEY for Little Musician separately (for $99).
I hope this helps clarify things for you!
P.S.
If you haven't done so already, do try out Little Musician first. You can download the software for free from your
Account > Purchases > Little Musician Software page. Upon installing it, you can play sample lessons and try out all PRO features for 14 days - once that trial period ends, the software will revert to Lite mode, but you can still play the sample lessons.