It is so difficult to make time for childbirth classes with today's busy schedules, I understand! While sometimes this can not be avoided and thus I am thankful that weekend classes are available, I prefer to teach a six week series for a number of reasons.
There is a lot to learn when it comes to preparing for labor and birth, and I feel that it takes time both to initially learn it, but also to process that new information. Having a week off in between classes allows women and partners time to think over what they've learned, apply it to their own situations and often, come up with questions to ask next week.
I have also found that for most people, it takes a length of time for them to internalize new ideas about birth, and "stacking" new information and affirmations week-by-week can help guide families as they discover these new feelings and attitudes.
Lastly, I think one great benefit of taking a childbirth class is to get to know and interact with other new families. Many of my past class participants have created lasting friendships through birth and into parenthood.