Jenafur,
It seems like the preschool program has some value to him at least motor skills and social. Also, it allows your DS2 to participate at home which is good for him. Maybe if you supplement your own instruction until DS has some testing done of his abilities? I know it must be difficult to get the level of instruction your DS needs, I was so oblivious to DD's giftedness that I just went along the regular curriculum and she read and learned on her own.
It would be fine though to speak with the teacher when she comes to your house about what the other teacher had intended for your DS. You can give examples of his abilities, and let her decide what she is comfortable with. If nothing happens with that, you can supplement at home during the days he is not at preschool.
