|Family||Liam (unknown close family relationship)|
|Book debut||Arthur's Eyes (book)|
|Cartoon debut||Arthur's Eyes|
|Voiced by||Walter Massey (s1-s18)|
Mr. Marco is one of the second-grade teachers at Lakewood, and was Arthur's teacher before he started learning under Mr. Ratburn. He is a kind teacher but doesn't tolerate any misbehavior from his students, and has zero-tolerance for cheating.
According to the episode, "Arthur and the True Francine", he once punished Francine for copying off Muffy's paper during a math test, although it was later discovered that it was Muffy who cheated by copying off of Francine, and she was punished instead.
Mr. Marco cares a lot about his students and does his best to give them a good education. However, he is very stern and will not hesitate to punish anybody who cheats in class.
The desks in his classroom are usually separate from each other in rows and facing the front of the classroom (unlike Mr. Ratburn whose classroom has groups of four desks that allowed the students' desks to face each other).
Mr. Marco dresses similar to Mr. Haney. He has light sky blue jacket with a yellow cream shirt underneath and a tie. He also has light sky blue pants and brown shoes. His coaching outfit is the same color but only a sweater and darker athletic pants with a white ball cap. In the early Arthur books, he was depicted as a moose with glasses, but the cartoon changed his appearance into an aardvark and removed the glasses.
- Arthur's Eyes 10101
- Arthur's Spelling Trubble 10202
- Arthur Accused! 10602
- Arthur's Baby 11101
- Arthur's Lost Dog 11202
- Arthur and the True Francine 11402
- Fern's Slumber Party 21502
- How the Cookie Crumbles 22001
- Revenge of the Chip 30502
- Arthur's Almost Live Not Real Music Festival 31102
- Double Dare 50102
- Don't Ask Muffy (Cameo) 70302
- D.W., Dancing Queen (Cameo) 80402
- Desk Wars (Cameo) 80701
- Buster the Lounge Lizard 150402
- Flippity Francine
- Crime and Consequences
- Mr. Ratburn's Secret Identity
- Mr. Marco's most prominent appearances were in Season 1, but he has appeared very rarely since then.
- In Arthur's Eyes, he has the same classroom as Mr. Ratburn, but in Arthur and the True Francine the walls were purple and there were dinosaurs painted onto them.