This is a problem. We already give high achievers poor service all the way from secondary through tertiary education. (In primary education most high fliers are able to demand teacher time through force of personality, and if they make it to postgraduate education, they may come into their own again).
So personalization seems to be the way forward as the best compromise between efficiency gain in a mass higher education system and serving the interests of individual students. Down with group assessments!
Group assessment: comparing group and individual undergraduate module marks. Assessment & Evaluation in Higher Education (2009) 34 (2): 141-148
This report describes a small study that analysed module marks of one cohort of science undergraduates from one academic year. It explored how group summative assessment marking affected the overall marks in comparison with individual assessment. A tutor allocated students to mixed ability project groups. Individual marks for the group work component were derived by tutor-, peer-, and self-assessment weighting. The results showed that students with high individual marks obtained lower marks in the group component. Similarly, students with low individual marks obtained higher marks in the group component. Study limitations, results and conclusions are reported.