As Long As We're Together (1) - S5-E1
Factual error: The start of season 5 took place in 1881 (the year Mary first went to the blind school). In 1881, Grace (born in 1877) would have been around 4 years old by then, but she is shown as a baby in the series.
Continuity mistake: When Mary and Laura dive into the lake to rescue the puppies they have their shoes on. As they are swimming around looking for them they are barefoot. When the get out of the water their shoes are back on.
Laura: I wanted to clean the blackboards extra good today, to make up for being late.
Mary Ingalls Kendall: And talking in class?
Laura: I was not talking.
Mary Ingalls Kendall: You were, too.
Laura: Was not! Nellie was talking and I was answering.
Trivia: Peter Billingsley of "A Christmas Story" plays Gideon in this episode. This was his television debut at age 11.