Continuity mistake: In season 1 (1957), Beaver is in grade 2 and Wally is 13 and in grade 8. Tony Dow was born in April 1945 and Jerry Mathers in June 1948. This means that Beaver/Jerry would have been 9 and Wally/Tony Dow 12, with a 3-year age gap. In the last (6th) season, Wally is a senior which indicates that he must have failed a grade. Meanwhile, Beaver is in 8th grade. Interestingly, the actors were also 3 years apart in age. At age 12 in 1957, Wally should have been in 6th/7th grade, which is more consistent with him being a senior in season 6.
Other mistake: In season 1, we learn that Beaver is in 2nd grade-Wally in 8th. So by the end of 6 seasons, Wally would be in college. Tony Dow and Jerry Mathers are actually 2 years+/-apart.
