Incubation period for chickenpox is 21 days, his teacher will have been infectious for a few days before she bacame ill/developed rash. I think he is likely to get it as well but you might need to wait for 3 weeks before you know for certain. Some children will have developed immunity to chickenpox from previous exposure to the virus whithout actually having been ill. DS1 had chicken pox fist, and DS2 had first blister on Day19, just when I had been beginning to hope he might have escaped it... More info about chickenpox
10-21 days after exposure, and she'll have been contagious/infectious (can never remember which is which) for 2-3 days before she got the spots. So earliest he could develop spots from this exposure is probably next Friday, and the latest Wednesday 4 November. However, if one or more of the other children have picked it up from her and they spend time with your DS he'll be exposed again and you have to start the clock again.
By no means certain he'll get it -- various of DS's friends had it at various points at nursery but he still hasn't had it (I think he is waiting for the most inconvenient possible time ).
DS's godfather came round on Jan 1st, three days later emailed to say he had the pox. He was advised there was a three week incubation period. Sure enough DS came down with on Jan 20th. I used Eurax Lotion. Worked really well minimised the itching completely. Only needed to apply it twice a day, and both DS and DD didn't scratch and get any scars. Calamine lotion tends to be a bit drying and not as effective for the itching. Make sure you put them in cotton clothes, keep them in, topped up with fluids and he'll be fine. He can go back after all the spots have dried. Generally att this young age it just makes them look worse than they actually feel. Good luck. xxx
I thought that too, the first, second, third and fourth times that DS was exposed . Then I decided he was probably saving it up until DD was born so that I could have two poxy children at once, but still nothing. If he still hasn't caught it by the time he reaches his teens I'll probably get him vaccinated privately, as it's Not At All Nice in adults.
I think there are two or three of them out of his nursery cohort who got through all the pox outbreaks unscathed.