http://www.fourmilab.ch/etexts/einstein/specrel/www/
ON THE ECTRODYNAMICS OF MOVING BODIES, A. Einstein, 1905: "From this there ensues the following peculiar consequence. If at the points A and B of K there are stationary clocks which, viewed in the stationary system, are synchronous; and if the clock at A is moved with the velocity v along the line AB to B, then on its arrival at B the two clocks no longer synchronize, but the clock moved from A to B lags behind the other which has remained at B by tv^2/2c^2 (up to magnitudes of fourth and higher order), t being the time occupied in the journey from A to B."

It follows from the postulates of special relativity that an observer in the moving clock's system would all along observe the stationary clock at B running SLOWER than the moving clock (initially at A). Accordingly, on the arrival of the moving clock at B, this observer would see the stationary clock at B showing LESS time elapsed than the moving clock.

The conclusion Einstein draws implies the opposite: on the arrival of the moving clock at B, the observer in the moving clock's system would see the stationary clock at B showing MORE time elapsed than the moving clock.

Clearly Einstein's conclusion ("the clock moved from A to B lags behind the other") does not validly follow from the postulates of special relativity. In 1905 Einstein replaced the valid argument (having as a conclusion symmetrical time dilation) with non sequitur whose conclusion, asymmetrical time dilation, implied time travel into the future (science died and magic was born):

http://www.bourbaphy.fr/damourtemps.pdf
Thibault Damour: "The paradigm of the special relativistic upheaval of the usual concept of time is the twin paradox. Let us emphasize that this striking example of time dilation proves that time travel (towards the future) is possible. As a gedanken experiment (if we neglect practicalities such as the technology needed for reaching velocities comparable to the velocity of light, the cost of the fuel and the capacity of the traveller to sustain high accelerations), it shows that a sentient being can jump, "within a minute" (of his experienced time) arbitrarily far in the future, say sixty million years ahead, and see, and be part of, what (will) happen then on Earth.. This is a clear way of realizing that the future "already exists" (as we can experience it "in a minute")."

Pentcho Valev