The graph to the right is a typical ‘Chances graph’, in this case for a student studying AS Biology. Chances graphs are based on prior achievement, and show the likelihood of a student achieving a certain grade. In the graph on the right, the most likely grade (and therefore the minimum target grade) for the student, as denoted by the black bar, is a grade C. However, 28% of students with the same level of prior achievement can expect to get a grade B, and 23% can expect to achieve a grade A.  
How can we ensure that the students in our care have the greatest opportunity of achieving these ‘above average’ outcomes? The work of Hattie and Marzarno is clear- we can look at evidenced based strategies that enhance achievement and ensure that they are applied in our classrooms.
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Subject Choice at A-level It is essential that we get students onto the correct courses and do simply accept a bums on seats policy. It is a reality that A-levels vary in difficult according to subject, although the variability seems to diminish at higher grades. The image on the right shows the average GCSE score defined by the University of Durham’s ALIS regression equations as being required on average to achieve grades E to A in different AS subjects. Would it not be unethical for us to not steer students with lower levels of prior achievement towards subjects that give them a greater chance of success ?
History, whilst powerful, is not the strongest influence on future achievement   Prior achievement throughout the educational life of an individual is a very powerful predictor of future achievement. Hattie reports an effect size of d=0.67 for prior achievement, strongly emphasizing it’s major role in influencing likely future achievement. Note however that Hattie only places prior achievement measures at 15th  place in his table of meta-analyses, and this is a crucial point: There are other factors directly under the control of the teacher that can positively influence the achievement of learners than evidenced through prior achievement studies. Schools and Colleges are increasingly being held accountable for the progress made by learners based upon their individual starting points. Value-added measures are calculated in comparison to average measures of progress according to prior achievement. Given that there is considerable evidence identifying factors within the control of Schools and Colleges that enhance achievement on a more significant level than prior achievement, it is ethically essential that such measures are fully explored. Failure to meet average Value Added targets is not simply a ‘missed target’, but is suggestive of an educational institution that has failed to respond to contemporary evidence about how learning can be maximised through adoption of evidence-based pedagogy. Chances Graphs:   
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