Mrs. Guppie is Tommy, Chuckie, Phil, Lil, and Kimi's science teacher, 9 years into the future. She is voiced by Monica Piper. She is also not one of those usual snobby teachers, and is the fourth grade science teacher. She is not seen later because now the Preteens are in 5th and 6th grade.
You can find Mrs, Guppie gallery here.