Capt Crash
As JF eloquently points out, there's a major difference between teaching your students to fly accurately and teaching them to land at the end of the runway.
Landing short on 05 at Cambridge is a fairly high-risk venture. You have a choice between Sainsbury's car park and the sewage works. If you land very short, you'll take out my house! So I have a personal interest.
Given that there's some 1670m from the threshold, and that Cessna 152s taking more than 1200 m to land are even rarer than engine failures on final, wouldn't you agree that it's sensible to pick an aiming point some way in to the runway (taxiway D always seems sensible to me)?