June says to Wally, "Well that's the first party Lumpy's had since you first started high school together!" But they DIDN'T start high school together. Lumpy was already in high school when Wally and Eddie arrived as freshmen. Several episodes discuss Lumpy being held back or flunking a grade, which eventually landed him in the same grade as Wally, et al.
After Ward complains about Fred being a "stuffed shirt", June comments, "Ward, Wally's best friend is Eddie Haskells and yours is Fred Rutherford. What's wrong with this family?" Wally's friend, of course, is Eddie Haskell (no "s" at the end).