Pupils who took part in a small-scale trial of formative assessment were left "gagging for their marks", research by Emma Smith and Stephen Gorard, of York university, found.
Some were so keen to receive traditional marks that they added up their number of correct responses in maths and vocabulary tests.
Supporters of formative assessment, also known as assessment for learning, argue that eliminating traditional grading of pupils' work helps to build their confidence and increases motivation A study by Paul Black and Dylan Wiliam, of King's College London, found that adopting it as classroom practice would raise GCSE performance by one grade per pupil per subject.
The Government is promoting assessment for learning through its key stage 3 and primary strategies, and sees it as one way of fulfilling its promise of personalised learning for all pupils.
But the York university study casts doubt over whether the national introduction of formative assessment will lead to any increase in standards. Researchers compared the performance of 104 Year 7 pupils in a comprehensive in South Wales.
They found that the 26 pupils who were given teacher feedback in place of traditional grades performed worse than their peers whose work was marked in the normal way.
The researchers said the results needed to be viewed with caution, however, because of the limited size of the study.