I won't say that isn't good for 9, as I had trouble getting back into tournament chess when I started playing again as an adult and had awful tourney results -- and that was better than what I was getting at the time. That said, that is decent for a beginner but can't say how common it is.
Ratings at the scholastic level are all over the place. The top rated active 9-year-old in the USCF is 2146 and the 99th highest (and a tie) is 1398. There are tons of players below that level at that age.
If he really enjoys playing and learning, getting a coach would possibly accelerate his chess growth.
My son (just turned 9) recently got interested in chess and started playing Scholastic chess in September2015. He has reached 1265 US chess rating by end of Jan 2016 (5 months) and around 36 rated games. He does not have a coach but I have given him some basic coaching, chess books and laptop. He also practices around 10 hrs a week. Is this a good performance which warrants me to take his chess seriously and get him coaches etc or is it common for kids to gain 1200+ points in 4-5 months ?