Answer:
The reason why Noah was able to hide that Jasper Jr. beat him up at the end of chapter 9 was that his body doesn't reflect any bruises.
Step-by-step explanation:
The reason behind this answer is that Noah is very smart and only allows Jasper to hit him in the stomach, a place that can't be affected with bruises. Also because he was able to anticipate that people were not going to search him in the hole body. Thus, this is the correct answer. Noah only allowed Jasper to hit him in the stomach to decrease the chances of evidence of the abuse.