Actor Allusion: Dom De Luise's character in "Gets Ready, Set, Dough!" is a baker, a reference to his second career as a gourmet cook.
Celebrity Voice Actor: Lily Tomlin was the voice of Ms. Frizzle, Malcolm-Jamal Warner voiced "the (male) producer," and the Theme Tune was sung by Little Richard. And then there's all the celebrities who voiced "guest" characters (Carol Channing, Dolly Parton, Dan Marino, etc).
The book The Magic School Bus and the Science Fair Expedition came out 20 years after the first book. As a result, it boasts a holographic cover, and includes appearances from several of history's most legendary scientists.
A DVD box set of the entire series was released in 2014 (20 years after the first episode).
A Magic School Bus Halloween did get a home video release however. Albeit a limited, VHS only one.
The Other Darrin: Arnold and Tim were originally voiced by Amos Crawley and Max Beckford, respectively; their voices broke after the first season and they were replaced with Danny Tamberelli and Andre Ottley-Lorant, respectively. (Crawley can still be heard as Arnold in the Title Sequence throughout the show's run.) Oddly, the voice actors for Carlos (Daniel DeSanto) and Ralphie (Stuart Stone) were not replaced after their voices broke later on, and neither were Tamberelli or Ottley-Lorant.
Out of Order: Season 1 Episode 1, Gets Lost In Space, had Arnold remark that the class had already been inside a rotten log and to the bottom of the ocean, but those field trips weren't shown until Episodes 04 and 06.
The Resolution Will Not Be Identified: The final episode "Take A Dive" was never identified as such. The only clue that it was the series finale is Ms. Frizzle deciding it was time for her to retire at the end.
Pluto is still a planet in "Gets Lost in Space", it's also depicted as being rather white, light grey, and blue, when in actuality Pluto is brown◊.
Pluto is also missing Nix, Hydra, Styx, and Kerberos.
More moons have also been discovered around the gas and ice giants since the episode and corresponding game debuted.
In "The Busasaurus," Ms. Frizzle says that Tyrannosaurus rex was the biggest meat-eater of all time. Too bad the discovery of the slightly larger Giganotosaurus was published in the same year the episode airednote Spinosaurus was considered to have been longer than Tyrannosaurus even during that time, but it still wasn't considered as massive. In the same episode, Ornithomimus and Troodon are both portrayed with scales rather than feathers.
Weirdly, "Gets Eaten" has Ms. Frizzle state that all food chains begin with plants, which had been a discredited fact since the discovery of hydrothermal vents in 1977, seventeen years before the episode aired. Even weirder, this error is pointed out in the phone segment, so it's not carelessness. The fictional producer's justification for excluding hydrothermal vents creatures is "Yeah, but they're weird."
A slightly better explanation for why they didn't include that in the show was that the majority of food chains begin with plants... and it's better to introduce children with a solid foundation of patterns before going into depth about all the exceptions.
As with most things of this nature, the computer episode went out of date the moment it aired. The fact that the computer has a "gajillion gigabyte hard drive" AND still has a floppy disk. While "gajillion" is not a number, we do have computers and networks capable of working on Yottabyte levels (10^24 bytes).
Also, WiFi would be used to connect a computer network today, rather than Ethernet cables.
In "Holiday Special," the whole plot revolves around an item being lost while the kids are sorting the school's recycling. As recently as 2007, many modern recycling plants no longer require manually-sorted inputs ("single stream recycling," a.k.a. one big bin for it all).