In Season 2, when Laura and Steve are paired together in marriage for a school project, Steve buys Laura a ring, which she rejects. Steve then sells it to Carl. However, in Season 9, when Steve proposes to Laura, he produces the same ring, saying he kept the ring over the years.
When Willie and Carl are talking in the diner, Willie asks, "Isn't that the kid that blew up the science lab at the high school?" Carl says "Yep, but that was years ago." Steve did not blow up the science lab though; Dexter Thornhill was the one responsible for the explosion. In episode sixteen of season five, Presumed Urkel, Steve was found to be innocent by a group of his peers when they discovered that he was set up by Dexter.
When Stefan proposes to Laura, the Season 6 Disney world episode is recalled. Stefan says that the reason he and Laura didn't get married at the time was because they thought they were too young. In the Season 6 episode, Laura sabotaged Steve's transformation chamber, so Stefan wouldn't be able to change back to Steve. Laura decided that she didn't want her relationship with Stefan to be based on this act of sabotage. It had nothing to do with their ages at the time.
The boom mic can be seen above Carl's head the first time Steve does his flamenco dance.