SOLVED. Juvenile Science Fiction. - Translation to the fourth (then fifth, etc.) dimension. [s]

[Robert]

A boy notices that one of the students at his school has changed in some way and investigates. He discovers that she(?) has a way of translating herself into the fourth dimension (portal in the cellar? father doing mathematical physics research?). She takes him with her. They have some sort of adventure with the four-dimensional people. Later they translate into the fifth dimension. Think they may continue for a bit. I think there was some sort of "odd-number dimensional worlds are technologically advanced, even-numbered dimensional worlds are more primitive" vibe. Perhaps a bit of a Jack-and-the-beanstalk feeling?

Read ca. 1985-1990.

[Rainbowheart]

The Boy Who Reversed Himself

[Robert]

You're scary-good at this Rainbowheart!

That must be it.

[Rainbowheart]

Lol, thanks! I did recognize this one because I've seen people talk about it before. Happy to help out. :)