Ty loved them! He started reading them at the end of 1st grade. We first listened to them as audiobooks and Ty was intrigued. So it was a great motivator to get him to work on his reading.
It was our goal to have him reading The Magic Treehouse series by the end of first. And he did it.

He read them at the end of first and throughout second grade. He learned so much from the books. But he only read the books on his own. I did not use the non fiction books with him.
There are Fact Tracker, non fiction books, that go along with the first 35 books. If I can get my hands on them - I have the first one on Dinosaurs - I plan on using them with Luc soon.
I will be reading the books to Luc as he's not as advanced a reader as Ty was/is.
Thanks, Robyn, for sharing about the Time Warp Trio. I'm always looking for books for Ty to read. He breezes through them so quickly! And I've never heard of this series. So thanks again!