During the tug of war between the boys and the girls over whose party to go to: the boys' team originally had George behind the Brain and in front of Binky, which George is later replaced by Alex when Binky decides to tie his team's end of the rope around his waist; and the girls' team originally had Fern behind Sue Ellen and in front of Prunella, in which Fern is later replaced by Jenna when Prunella then ties her team's end of the rope on the jungle gym after the boys do their part first.
When the grandfather clock hits 12:00 PM for when Muffy should arrive at Arthur's house for the party, it plays the 4-note rhythm that should only be heard when the minute hand is pointing to 15, but nonetheless strikes up to 12. If the minute hand is pointing to 00, it should play the 16-note rhythm and then strike by counting based on the numbers from 1-12 the hour hand is pointing to.
In "Francine Frensky, Superstar", even though Francine should be on the stage performing, she can also be seen in the audience watching the performance in some shots.
In "Francine Frensky, Superstar" Francine's older sister Catherine is first introduced here, but their bedroom that they share only has one bed in this episode that belongs to the younger sister. This was remedied in the TV series' later episodes focused on Francine and/or where the inside of their apartment is shown.
In "Arthur's Birthday", in a close-up shot, Muffy is seen holding a stack of party hats, but wearing a white long-sleeved shirt she wears underneath her dress she casually wears in the series, even though she should be wearing her short-sleeved shirt that's part of her party attire she wears for the entire scene of the birthday party. Mrs. Read is also seen to pick up one of the hats, but with looser-fitting sleeves than what she's supposed to have for her sweater.
When Francine's classmates decide to teach her a lesson about her actions on how she has their costumes set up after she rejects Arthur's advice on how they're outraged, when Muffy says "Me too" and the Brain says "Me three", the latter's hand is miscolored pale when his complexion himself is brown.
The Brain's family's ice cream shop has one window with one door next to it on its exterior. In the interior shots, it has the door in the middle between two windows that should be for Jack's Joke Shop next door.
When Francine swings her bat to hit the clown piñata, she positions her hands like a right-handed batter, but swings in the direction a left-handed batter would swing.
It would not be age appropriate for children to be gifted a spin-the-bottle game, which Francine gifts to Arthur. This same thing happened in the book it was adapted from. This kind of game is for teenagers and over since it involves kissing and implies sexual behavior that kids should not be experimenting at such a young age.
When D.W. chases Arthur with her "pinch to grow an inch", Arthur is heard yelling "MOM!"; but his mouth doesn't move when he says this while he and D.W. run across the screen.
Fern received invitations to both Arthur's and Muffy's birthday parties before they were later consolidated to take place at Arthur's house, but it is unknown why she didn't attend in this episode; even though she did in the book this episode was adapted from.
In "Arthur's Birthday", the titular character's birthday is May 25th just like the book it's based on. When D.W. brings up her own birthday, her brother informs her that it isn't for six months. In the later episode "D.W.'s Perfect Wish" from Season 3, her birthday is March 1st; therefore, Arthur should have said her birthday isn't for ten months or that she already had it a couple months ago.
In the beginning before Arthur leaves for school to hand out invitations, Grandma Thora asks Arthur what kind of cake she would like to bake, which he responds "Chocolate!" which implies her to be a good cook. In the later episode "The Half-Baked Sale", she is revealed to be a poor cook.
Baby Kate is shown as a 1-year-old toddler during the timeframe of this episode being set on Arthur's and Muffy's birthday on May 25th near the end of the now 8-year-old kids' 2nd grade year. Yet "Arthur's Baby" and "D.W.'s Baby" where Baby Kate is born are set presumably sometime during the first semester of Arthur's second grade year, so she shouldn't have the capabilities of a toddler in this timeframe.