I wish I had been a part of this live webinar! Here is what I would have said if I were involved. 
Intro – I am currently an Algebra 1 teacher (formerly middle school math, 3rd grade, alternative school grade 6-12 math)
1 – Kids in general don’t like to fail. Instilling growth-mindset is hard because students don’t want to fail AND they don’t want to work too hard, a.k.a ‘think.’ Breaking students from just ‘doing as their told’ and transitioning them into being active thinkers in charge of their learning is tough and scary for students. Providing an atmosphere where mistakes are okay is crucial to student-centered learning.
2 – @mlschnick , I totally agree with the setting up kids to ‘fail.’ Making mistakes is how we learn. [MATH - Math Allows Thinking to Happen] I purposely set up problems where there’s more than one way to get to the answer, or where there’s even more than one answer possible. I also believe that student choice is a big component in student-centered learning. I recently had three out of five classes as ‘repeater’ classes; they failed semester 1 so they are repeating that section of content. There were lots of behavior problems at the beginning because they assumed my class would be just like their other math classes they’ve ever had. Once I introduced my ‘tracking’ sheet to the students, behavior problems became a non-issue. The tracking sheet took all the concepts for the semester and grouped them into several learning strands. Each strand built up to the test(s). Students got to choose which strands they worked on. If they were on a roll for strand 1, they could keep going in that strand for that day. If they got ‘burnt out’ or started to get lost at a certain point they could switch strands. The only set criteria was completing X number of GoFos per day.
– Feedback is another important component for student-centered learning. I love Formative for the immediate red/green indicators, but also because I can give more specific comments as feedback in the assignments. @david, hopefully, Formative opens up the ability for students to reply to that specific feedback.
4 – There are several challenges with student centered learning in math – math is fairly linear; you have to know X and Y before you can learn Z. I agree with @brent.hall about not having enough time for students to explore, learn and share. Time is my absolute worst enemy given my student population. {Two out of three students are truly not ready for Algebra 1, but the state requires them to take the class their Freshman year.) I also agree with @mlschnick about meeting all students’ needs, especially when they are at such different learning levels. I find that if there’s enough of ‘me’ to go around, then I don’t have behavior issues. I tell the students that Formative is like having a mini-Mintner on their shoulder telling them if they are right/wrong. I also agree with @apadilla about freedom & distractions – In my repeater classes they had the freedom to choose their strands as well as the freedom to choose when they were ready to test. Unfortunately, it was harder to tell when they were on-task because everyone was doing something different. Phones and music became a problem early on, so I had to have students earn the privilege of music daily! They couldn’t listen to music until they had completed one GoFo with at least 70% accuracy. I found that it helped them focus on getting started, and once they finished one, they were more likely to continue working even with their earbuds in. @mlschnick , you asked for suggestions for online ‘paper airplanes’ – What about having one Google doc with a table of problems or links to other Google Docs? Each group is assignment a problem to work. When time is called, digitally ‘throw’ the plane by clicking the ‘next’ hyperlink at the top/bottom of the page. Students can add comments/suggestions/corrections to the work that’s there. You would just have to make sure that the sharing options are set right so students can have editing rights and so you don’t force ‘new copies’ each time the document is opened. You would also have to have a new set of documents (and links) for each class – or be prepared to save a copy of the work before you ‘clear’ it for the next class.
5 –I’m going to attempt to gamify my class next year by turning the tracking sheet into XP and having students level up (similar to @mgarcia). I also would like to make a digital version of the tracking sheet with hyperlinks to my GoFos that allows students to have their own personal copy that can be ‘filled’ in with color as they complete assignments. I’d also like to explore alternative forms of re-assessment for those who failed the paper/pencil version the first time; on paper, orally, using whiteboards, make a video presentation, etc. (Other ideas that would be conducive to math are welcomed.)