I saw School of Rock from the front row (thanks to the lottery). I did, however, see Rocky from the last row of the mezzanine. I thought that the view was fine. Just try to go with the more centered seats on the mezz if you can.
"There’s nothing quite like the power and the passion of Broadway music. "
As someone who works there I can tell you that generally the mezzanine is better. I got my friend front row center tickets of the mezzanine, and they couldn't have been better seats.
The thing to look out for is how off to the side the seats are. The theater is very wide and some of the far seats are actually obstructed in both the mezzanine and the orchestra (although usually they are sold as such).
Also keep in mind that SCHOOL OF ROCK is a rock show and is therefore very loud at parts. You might want to avoid being too close to the stage in the orchestra (especially on the sides near the speakers) if you think that is going to be a problem for you.
I saw this tonight and I'd definitely pay attention to Broadway Guru's comment. I was in row Q of the orchestra (so not that close even) and had a little trouble understanding the lyrics sometimes because of the music. I got used to it but I have good hearing. I imagine if you have a tougher time hearing the mezz might be a better choice.