http://www.people.fas.harvard.edu/~djmorin/chap11.pdf Introduction to Classical Mechanics With Problems and Solutions, David Morin, Cambridge University Press, Chapter 11, p. 14: "Twin A stays on the earth, while twin B flies quickly to a distant star and back. (...) For the entire outward and return parts of the trip, B does observe A's clock running slow, but enough strangeness occurs during the turning-around period to make A end up older."
That is, the travelling twin is getting older than his sedentary brother all along except for the short turning-around period when some strangeness occurs... What strangeness? John Norton explains:
http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/spacetime_tachyon/index.html John Norton: "Then, at the end of the outward leg, the traveler abruptly changes motion, accelerating sharply to adopt a new inertial motion directed back to earth. What comes now is the key part of the analysis. The effect of the change of motion is to alter completely the traveler's judgment of simultaneity. The traveler's hypersurfaces of simultaneity now flip up dramatically. Moments after the turn-around, when the travelers clock reads just after 2 days, the traveler will judge the stay-at-home twin's clock to read just after 7 days. That is, the traveler will judge the stay-at-home twin's clock to have jumped suddenly from reading 1 day to reading 7 days. This huge jump puts the stay-at-home twin's clock so far ahead of the traveler's that it is now possible for the stay-at-home twin's clock to be ahead of the travelers when they reunite."
Again: During the short turning-around period, "the traveler will judge the stay-at-home twin's clock to have jumped suddenly from reading 1 day to reading 7 days"! But this is an idiocy - the turning-around period is OBVIOUSLY of no importance:
http://www.damtp.cam.ac.uk/research/gr/members/gibbons/gwgPartI_SpecialRelativity2010.pdf Gary W. Gibbons FRS: "In other words, by simply staying at home Jack has aged relative to Jill. There is no paradox because the lives of the twins are not strictly symmetrical. This might lead one to suspect that the accelerations suffered by Jill might be responsible for the effect. However this is simply not plausible because using identical accelerating phases of her trip, she could have travelled twice as far. This would give twice the amount of time gained."
http://www.informaworld.com/smpp/content~content=a909857880 Peter Hayes "The Ideology of Relativity: The Case of the Clock Paradox" : Social Epistemology, Volume 23, Issue 1 January 2009, pages 57-78: Albert Einstein quoted to have written in 1911: "The [travelling] clock runs slower if it is in uniform motion, but if it undergoes a change of direction as a result of a jolt, then the theory of relativity does not tell us what happens. The sudden change of direction might produce a sudden change in the position of the hands of the clock. However, the longer the clock is moving rectilinearly and uniformly with a given speed in a forward motion, i.e., the larger the dimensions of the polygon, the smaller must be the effect of such a hypothetical sudden change."
Why do David Morin and John Norton refer to the strangeness that occurs during the turning-around period? Because, although in 1911 Divine Albert said that the turning-around period was of no importance, in 1918 he found it suitable to say that the turning-around period was of utmost importance:
http://en.wikisource.org/wiki/Dialog_about_objections_against_the_theory_of_relativity Dialog about Objections against the Theory of Relativity, Albert Einstein 1918: "According to the general theory of relativity, a clock will go faster the higher the gravitational potential of the location where it is located, and during partial process 3 [traveller sharply turns around] U2 [the travelling twin's clock] happens to be located at a higher gravitational potential than U1 [the sedentary twin's clock]. The calculation shows that this speeding ahead constitutes exactly twice as much as the lagging behind during the partial processes 2 [traveller moves with constant speed away from sedentary brother] and 4 [traveller moves with constant speed towards sedentary brother]."
So half of the Einsteinians teach what Divine Albert said in 1911, the other half teach what he said in 1918: