IMHO (in my humble opinion.) And good that you've read that part. It's the heart of what CLAD exists to communicate. Beyond that, I'd say not to get too snarled up in who theorized what and when but rather to seek to get clear on how people learn to speak a second language, what we have found works best in helping them to do so, and how that might be applied in both EL and SDAIE classrooms at several levels. It will also be helpful to you to review the California Standards for ELL: What can children at level X in grade Y fairly be expected to manage with regard to English language acquisition?