I once heard about a conversation between a secondary and elementary teacher. In awe, the secondary teacher made a comment about all the things an elementary teacher is responsible to teach in a day, to which the elementary teacher responded with, "That's what scripted programs are for." That response both dumbfounds and saddens me. Indeed I have a mountain-load of material to daily teach my first graders, but I don't believe that's reason enough to hand over the professional decision-making process in my classroom to a collection of strangers who have scripted my teaching for me. Even after starting my 20th year of teaching, I don't claim to be an expert at creative and authentic lesson planning, but I know the struggle and challenge is worth it. I'm not one to surrender when I know what's right for my kids. If I find myself in a conversation with someone who is in awe of how much I teach in a day, I'll smile, shrug, and say, "It's just what I do."
P.S. I do use Lucy Calkin's Units of Study. She's definitely onto something. I don't use them verbatim though. I tweak and use them as a guide just as she would want me to.