The 16-17 year old saver card decriminates against students who are born early in the school year. For example a child born in November has to start paying full price fares to get to school /college from their 18th birthday whereas someone born in July gets it free for the whole 2 years of a levels /college. By changing it to a 16-18 saver card all young people in full time compulsory education get the full half price rail travel.