I'd agree about not worrying about testing for science and history. There's no such thing as a "grade level" for those since it's not something like reading where there's an "easy" level where you can easily measure as things are getting progressively more difficult. There are just different topics, and the topics covered in different grades will vary COMPLETELY by what school system you're in.
Heck, do young elementary grades even cover history at all in most schools? Maybe some American history in US schools, perhaps... But not really all that much. And the "science" will tend to be things like... weather can be rainy or sunny or snowy, seeds grow into plants when they have light, animals are living and rocks are not, we have five senses... Pretty basic stuff, MOSTLY which kids would pick up on their own just interacting with nature (given enough nature exposure, of course...)
For reading evaluation, I'd suggest the Schonell reading test. It's online in several locations. It's just a list of words, progressively getting more difficult. The child reads them in order, no second chances or sitting sounding them out for minutes -- they can take a moment to figure it out but have to move on if they don't know quickly. It starts with "tree" and ends with things like "bibliography" and "metamorphosis".
Then you count how many they got right, divide by ten, add 5, and that's their "reading age".
When DS was young, we'd stop partway through when he started getting frustrated with the difficulty of the words. As he got more advanced, though, he was keen to at least TRY every single words, and it was fun when he'd actually figure one out. He's consistently scored about three years above his physical age, which I think is accurate, so I trust this test.
There are other similar tests out there too. One involves reading in columns until you reach a column where they get more than 3 words wrong, and that's their grade level... something like that anyway.
Anyway, here's a Schonell test link:
http://members.tripod.com/~gleigh/readtst.htm