Heaping praise on pupils in the classroom for good work may not help them improve their marks, according to new research.
Pupils can be made to feel teachers had little faith in them to begin with if they are laden with compliments, a report by the Sutton Trust education charity found.
Praising students and allowing children time to reach the answer on their own are two methods frequently used by teachers which are not backed up by evidence, according to the research.
Instead, quality of teaching and the teacher's subject knowledge are the two factors that make the biggest difference in a child's academic achievement, the report said.
The study, produced by Durham University for the Sutton Trust, is based on a review of more than 200 pieces of research on how to develop good teachers.
While giving pupils praise could be effective, in some cases it could be counterproductive, the study said.
It examined a number of common teaching methods to see if any of them made a difference to results.
Popular teacher strategies there is 'no evidence' to support:
"Discovery learning," in which pupils find out ideas for themselves
Attempting to boost pupils' motivation before teaching a lesson
Presenting children with information in their own preferred learning style
Surrounding children with pupils who are at the same academic level
Professor Robert Coe of Durham University warned anyone who wanted to judge the quality of teaching that the profession was "surprisingly difficult" because of its "complexity":
Great teaching cannot be achieved by following a recipe, but there are some clear pointers in the research to approaches that are most likely to be effective, and to others, sometimes quite popular, that are not.
However, top head Susan Papas was sceptical about not praising children.
While the no-nonsense head, who banned parents from smoking at the school gate, felt the Sutton Trust's report made "some interesting points", she felt it was "important" to praise children for good schoolwork.