There are A LOT OF mistakes. The questions and answers don't even match and their "correct" answer is many time wrong. Then you blsme your child because s/he doesn't pay attention to the details in the text.
Many grammar mistskes.
Synonyms – well, there is no dictionary on this planet that can prove that the answers, that Achive 3000 gives you, are actually correct. My child is often confused because the website shows the most ridiculous answer as the correct one.
Overall, I feel like the authors of the questions should take ESL classes. Or stop drinking whatever they drink.