My ds read the series at the start of 2nd grade. His teacher used accelerated reader tests when he finished each book. She also had him write a summary on the content of each book when he finished. She was the coolest teacher.

The series didn't bother him from what I know, now a book or movie on germs or bacteria outbreak and he gets all weird.

He is now 11 and we still read every night. I get to pick the books. I will continue reading to him as long as I can.