My ds, 5yo in 3 weeks, finished K with flying colors and is reading the books in the emerging readers pack on his own (we already owned half the books!). He has fabulous listening comprehension skills, even if he is still making sense of the world around him (his conclusions can come out of left field sometimes). He is writing fine and starting copywork with minimal help (I sometimes dot out the letters for him to help him with form, but he can do it on his own.) According to your Placement Chart, he is solidly in Beyond the whole column (minus the age).
My dd, 7.5yo, finished 2nd grade with straight A's, though a lot of information wasn't retained (ahh, the joys of textbooks). According to your Placement Chart, she is solidly on Bigger. Though, referring to my retention issue, I will have to take a close look at the spelling list 2 versus dictation list 1 to determine where she falls on this. She IS ready for dictation because she has been doing it this past year in Writing & Grammar.
Okay, no brainer, they do their own right pages. But I REALLY want the left page to be family learning. I want to embrace homeschooling. I want to streamline where ever I can so I can also enjoy time with my new baby girl (proud, happy, and over the hills in love mama here). What are your thoughts and suggestion as to WHICH left page to use? Does it really matter?
Along the same lines: science. Science is on the left page for Beyond and the right page for Bigger. Which science? Maybe both because my dd is a science enthusiast? Only 1?
That should do it for this topic. I have 1 more question but it deems its own thread.
Blessings to all my wisdom sharing educators!
Laurie Beth
, I'd say that since he is below the target age range for Beyond, combining the 2 of them in the left side of Beyond would be the best fit. The left side of Bigger Hearts is challenging - I wouldn't do it with anyone much younger than 7 yo. 
You can challenge your 7 yo with the right side of Bigger, and that will be a great fit. I'd do the science in Beyond, because we enjoyed the links it has with the history being learned, and in Bigger Hearts (as well as subsequent guides), the science links even more to the history, so it's nice to do the science and history together in the same guide if possible. I'll be doing the second half of Beyond four days a week this year with my little Riley, so we'll have to swap stories! 
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Just wanted to pop in! Pretend like my smilie is waving!