Most kids I've seen are reading mostly sight words, or beginner readers in first. There are some that cannot read still however or have minimal reading skills going into 1st ( some states do not mandate K at all ). If he is going to a Magnet School for GT, I would highly suspect most if not all can read some, and a lot will be reading at a higher than grade level.
My DS8 (birthday today yey!) was reading Harry Potter by the time he entered Kindergarten but now going into 4th grade, last year he still had friends that were struggling readers so not everyone has an easy time learning it.Writing wise, most can write their letters and form small sentences by first in an average school...although some are still hard to decipher, and spelling levels are all over the board.
What would worry me is the G&T school and their learning pace...have you contacted them about what their grade level expectations are for 1st so you can see where your son falls, especially since he is young. I can't believe a private GT school wouldn't teach reading...thats um...shocking really!
Have you tried getting him to play around on
www.starfall.com ? Do you have an ipad that allows apps that have finger writing programs? Also dry erase marker boards with letters to trace, and small sentences, work books with lots of characters that make things look more interesting?
All my my sons have used starfall while learning to read. My 4 year old twins currently play on it daily for the reading section.
How are your sons other educational areas ( math, etc)
Good luck, I'd say start by asking what the level going into 1st is, and see if its a good fit for your little man.