A good piano teacher is way more helpful than any software.

Band-in-a-Box cannot assist your son's playing developing expression, phrasing, musicality in the sense of what's between the notes on your son's staff lines.

Band-in-a-Box may motivate your son, though, having fun playing along with a band - even within his own shed or something. His playing would need to be somewhat solid for this purpose, though, since Band-in-a-Box is like a metronome quite sturdy in its timing. This may potentially hamper your son's motivation. Band-in-a-Box does not listen to his playing - as would a live band or other software concepts such as the -> Smartmusic approach.

Irrespectively of the potential caveats, Band-in-a-Box has great educational value. It comes with a great library of songs, often played by beginning instrumentalists. Just look at the leadsheet of "Für Elise", say, and capture its harmonic underpinnings at a glance. This alone may be a worthwhile support of otherwise classical piano teaching.

Martin