I always think of science as being such a broad area. There is always more to do sideways. If they learn about the cell and mention that the mitochondria are the cell power plants, the young scientist asks: "In what way? What is the mechanism? How does my apple become energy in a cell?"
So, the best area for outside enrichment isn't in the direct experimentation or even in the content, it is in the ways of thinking like a scientist of asking the big questions. Help your DS enrich for himself as he sees fit. If they are doing typical "rain forest studies" in schools, he could read a book on it himself. Ask questions like: where are rainforests? etc. They do an experiment to test one factor, he can think of more factors. Better ranges of values to test, etc.
Then maybe you ask the school to get out of his way and let him find resources to support his studies adjacent to the school's curriculum. (and then the teacher doesn't have to be creative, just help with a few questions and double-check work as needed.)
Then again, I don't how ready that sort of self-enrichment is for a 7 year old as I don't think mine is quite ready to do it in science himself.
