Elsewhere I am attempting to introduce SR to people with high school maths and high school concepts - my qualification for this being that all I have is high school maths and high school concepts. My 'view' is that you can pitch high school maths and high school concepts at someone with high school maths and high school concepts and there's a reasonable chance they'll hit the ball. In the context of this forum the 'game' is to get the other guy to hit a home run (assuming that's good - I have no idea how baseball is actually played). To get a home run (I hope this is correct) the batsman has to (at least) hit the ball.
Within the concepts of high school I maintain that an observer cannot 'move' - he cannot observe from anything other than his frame and within that frame he is (by definition) stationary. By all means introduce a remote book-keeper, but later, much later.