To calculate the overall star rating and percentage breakdown by star, we don’t use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyses reviews to verify trustworthiness.
I do not recommend it. Scary pictures and a lot of "oooohh, pffff, boom, gggggrrr" on each page, and filled with useless american expressions, it will bring no value add to your child's reading comprehension, nothing to learn from it.