We have had issues with lower school science because sometimes it is simplified so that what they are taught isn't strictly correct.
Year 7 DS likes to discuss his homework with older siblings (who are 'science specialists') when they are about, so he can go into more detail.
A few times this has resulted in him taking issue with what they are taught in class. Fortunately he has a receptive teacher but at least once he has had test answers marked as incorrect because it wasn't what was expected although it was techincally correct.
If you want to be sure of explaining topics at the correct level for the curriculum then there are quite a few study/revision guides available.
If children are interested in/ have a flair for science then sometimes they find the early stuff confusing because it doesn't deal with topics in sufficient details to answer their questions. We get lots of 'yes, but what if/ but surely.'..questions.
Thankfully I call in expert assistance - well if DS is going to eat me out of house & home during Uni vacation he can do something useful