If all of your protagonists had to take the SAT's and the GRE's, who would score the best? Who would score the lowest?
For everyone on his list, we have to assume that they don't get questions that are impossible for them to answer. Like questions relating to Earth's literature or technology.
Yerin would score the worst, as she's illiterate and would have no idea what to do with the tests.
Simon would be second-worst. His parents only cared about his education until the events of the HoB prologue, when he was eight years old. After that, the only math skill he exercised was counting, and he rarely wrote anything besides his name.
Calder is next up. He received a noble education, thanks to his mother, but not early in life. He would score better in math than in English (assuming we translated the fictional Imperial language he actually speaks into English), and his scores would be decent in both categories.
Leah would do better than Calder, but not much better. She's extremely well-educated, but to the limits of her time period and world.
Lindon's education is more suited to standardized tests; he actually learned math and linguistics (obviously he's not speaking English, as none of these characters are) from textbooks, and while his scientific education is either not applicable to our tests or is downright wrong even by Cradle standards, his mathematical and language skills are solid.
Shera would do the best. Gardeners got a great education and she has a well-trained memory and a precise mind. She would score higher than any of my other protagonists.
...if she could be bothered to finish the test.