Any doubt about that? Let me repeat. No. No matter how much one individual might wish to sell a grammar-based agenda, and wish to put words in my mouth to support his agenda, TPRS does not support explicit grammar teaching. Nor does it need it. Nor would explicit grammar instruction improve TPRS, as an addition or otherwise. Full stop.

Honestly, I’m getting a little tired of the effort to claim solidarity with TPRS in an attempt to further a grammar-centric agenda, which has been well documented through efforts to sell such a program (literally sell).

The individual recently commented on a mailing list:

What do I personally think about explicit instruction’s value? I pointed this out before: Terry Waltz seems to have had great success with her beginning Chinese students in using tones through her innovative grammar explanation. The results seemed clear, even to the point of surprising her colleagues. These noticeably improved results, appear to be attributable to her explanation/system.
My colleagues were not using: Tonally Orthographic Pinyin, directional gestures, and concentrated optimized immersive input in the form of 100% comprehensible language. They WERE using explicit explanations.
This has been my main point all along: the kind of explanation matters (on the scale of more effective and less effective). Yes, saying “The sound goes up, it’s green like a tree growing up to the sky!” is definitely explicit grammar instruction in phonetics. As I said very early on, this is precisely the kind of explicit grammar instruction we need. From my perspective, she has shown that grammar instruction should be innovative and improved, not abandoned. 
This person doesn’t know what an explicit grammar lesson is. Explicit instruction is giving students a rule, then asking them to practice it, hoping that the practice and application of the rule will lead  to mastery. What we do in TPRS is to expose students to language, and ask them to understand and respond to it, knowing that this will lead to acquisition. We do a small amount of explicit linkage between meaning and form, which is the linkage that builds an internal grammar (please look up how this word is used in linguistics). We call attention to features of text or words after they are “in play”, not before.
From my point of view, she has single-handedly debunked the proscription of explicit explanation, and clearly demonstrated the effectiveness of good explanation. How could anyone disprove, let alone want to disprove, that it doesn’t help acquisition?
I have done nothing of the sort, because I’ve never used explicit explanations. I present language in context and point out features when students ask about them. This includes tones and Pinyin spellings — they are not pre-taught, they are only pointed out when the students ask — which only happens after they are comprehending the meaning well enough to have enough mental resources left over to do so.
And I would do the research to prove that TPRS itself didn’t help acquisition, if I saw evidence that was true. I am not a brand ambassador. I’m simply using the tools that best fit what the research tells us at this point, which is Comprehensible Input. Of the methods that claim to be CI-based, I believe TPRS currently is the best fit for the research for use with novice students.