teacher centered vs student centered instruction role in K-12?

What is the difference between teacher centered and student centered instructional strategies? What is the appropriate role of each strategy in K-12 eLearning environments? (Instructional Technology and Media for Learning).

First the definition of teacher centered instructional strategies with my example of each:.
Here is a lesson on how exponential curves are used in real life. I used many of these activities in my actual classroom, High School Algebra 2.

Teacher Centered:

• Presentation- Giving the students the formula for a tsunami and explain what the variables mean in a real life situation. - (http://www.pppl.gov/events) Disastrous Equations: The Role of Mathematics in Understanding Tsunamis
• Demonstration - What does this sign mean? (Have a tsunami sign printed out and taped to the classroom door so students can read it to start the conversation about tsunamis as they walk in the classroom.) (Http://pubs.usgs.gov/circ/c1187/c1187.pdf)
• Drill and practice - Practicing the exponents of 10 with flash cards (each exponent is 10 times more powerful than the next.) Explain the Fujita scale.
• Tutorials- Watch a video on the Japanese Tohoku Tsunami or the Indonisian Tsunami of 2004 (http://www.pppl.gov/events)

Student Centered:

• Cooperative Learning- Take turns timing a friend with a watch.Use the same distance, two blocks, then take an average of how long it takes to run two blocks. Do the same for your friend. Write your results in a table.
• Games-Pan Balance-Expressions ( http://illuminations.nctm.org). Use the pan balance game to try out different numbers. What happens to the graph as the numbers get larger?
• Simulations- Math walk: go outside and watch an airplane in the sky. Use a watch or stop watch with a second hand to time how long it takes the plane, from the time you first see it until it is outside your vision. Do this two to three times to get an average speed.
• Simulations-Build a tsunami experiment. http://www.youtube.com) How tsunamis work-Alex Gendler which has great graphics. Tsunami; project by first grader Bianca, watching this demonstration would be great for the many hands-on learners. They can build their own tsunami box.
• Problem Solving-Do after you have practiced with the pan balance. Using a graphing calculator enter the formula for a tsunami ( y=  x*9.8) . What does the curve look like? Draw a picture in your math journal. What conclusions can you make looking at the tsunami curve?
• Discussion- Would you have time to run from sitting on a seashore playing in the sand to a safe two or three story building when a tsunami happens? Explain your answer using the table you have made when you were timing yourself and the airplane. Why or why not? How much warning would you need? What devices could give you a warning? Would you be worried about the tsunami if you were on a boat in the middle of the ocean? (http://pubs.usgs.gov/circ/c1187/c1187.pdf)

In a K-12 eLearning environment a teacher needs to make informed choices. The teacher needs to choose eLearning activities that are appropriate both mentally, and emotionally for the student. The teacher needs to address the different learning styles of students.
One web site I found is addressed to High School students. The other web site I found was addressed to 1st graders, but it could be adapted to High School students. Although, I would highly recommended blocking all comments on any web site that I as a teacher would post for my class.
With a teacher centered instructional strategy the teacher has more editorial control over the content of what activities the students are doing. A teacher can control the environment where a student is doing eLearning. Even on the internet there needs to be firewalls, virus protection and constant monitoring of what a student is doing on the internet. For example, a teacher can encourage a student to go on a math walk but the student also has to be supervised on the playground or school grounds.
With student centered strategies in eLearning a teacher needs to be an editor because some things are not appropriate for a school setting whether learning is through an on-line or a face-to-face format.
I absolutely am not a shrinking violet. I've lived too long, and seen too many things in my life that are rude, disgusting and appalling. Whether voluntary or involuntary just by being alive. I was very concerned when I was doing research on the various internet sites about how vulgar and rude many comments are in some of the really good instructional videos I found. I was appalled at the negativity shown to the 1st grader and her tsunami project. (http://youtube.com) Tsunami: Project by 1st grader Bianca. No wonder teachers have to worry about bullying, not only from students but from adults who cannot be civil.
Yes, I understand that the internet is literal fair game for anything goes, but sometimes mean people go too far. I was curious about how to eliminate the comments from the screen, so I asked the editorial board at You Tube if there was a way for a viewer to turn off comments, but still watch the video. I know the moderator can turn off comments but I wondered if a viewer could? I am awaiting their feedback. As a teacher I would not want my students exposed to demeaning vulgar comments in my classroom. They get enough of that outside the classroom. The only solution to this problem is to use the teacher's computer, then project the video to the class in full page format so the students could not see the comments
I am an adult so I can take mean vulgar comments and take them for what they are, but that earnest little 1st grader cannot. She's so excited about her experiment. Would these comments hurt her feelings so much so that she will stop exploring the world of science like so many other girls have done?
When I taught this unit I also used the front pages of the newspapers, news magazines and I had access to news feeds over my TV set in the classroom. It just so happened that we were studying a unit on exponential and logarithmic curves during the 2004 Indonesian Tsunami. I had a case of graphing calculators, and a portable laptop lab. The NCTM web site was on our approved list of safe sites. The students were surprised to find out that a tsunami travels just about as fast as a jet plane. They also found out that if they were ever in one, they better run as fast as they can to higher ground or a high building.
What about posting student work? I recently read The Elements of Blogging by Mark Leccese and Jerry Lanson, who recommend moderated comments when doing a blog. I would think that any video or blog involving student's work should be posted without comments. That way bullies, trolls and hotheads would be eliminated from the discussion.