My stepson started pre-K all in Spanish and they worked in English a little every day, increasing gradually. By 1st grade he was in all-English regular classes. However, my stepdaughter started pre-K all in Spanish and by the end of 2nd grade was not fluent in English. She was moved into all-English classes in 3rd grade and found it very difficult.

The difference between these two children, I believe, is completely because my stepdaughter basically got no English input other than that small amount during the school day. My stepson had a lot more English input at a younger age because of family changes (English speakers coming into the family).

I would agree with Simona that 3rd grade is a bit late to introduce a language if there isn’t any other exposure happening in the environment. If you live in an English-speaking country it would be perfectly fine, because he will be get a lot of input in the environment. But if school is the only place your child hears English, they should be provided some regular exposure to it between now and 3rd grade when it starts at school, and it will need to be more than an hour a day to achieve fluency.

My father went to kindergarten in 1945 in a rural community in the USA where everyone was still speaking their German since the 1830′s, but in that year when WWII ended the schools changed to an English-only policy. English was also encouraged amongst the people to be used at home. Within a couple of years he was no longer able to speak German and by the time he was an older child, not even understand it.

So I would be concerned that if your son does not hear English from age 4 until 3rd grade, he may have little memory of it. I would also say that 1 hour a day, from my stepdaughter’s experience, is not enough to get to fluency.