a little encouragement goes a long way, but a new study suggests that lavishing praise on pupils is unlikely to help them improve in the classroom.
Instead, it can leave young people feeling their teacher had low expectations of them.
Praising students is one of several popular methods used by teachers that are not backed up by evidence, according to a new report.
The report indicates that the two factors that make the biggest difference to boosting pupils' results are simply the quality of teaching and the teacher's subject knowledge.
The study, by Durham University, is based on a review of more than 200 pieces of research.
It concludes that heaping praise on pupils is often seen as positive, but studies show it can also be harmful.
Praise that is meant to be encouraging and protective of low-achieving students can give a message of the teacher's low expectations, the report found.
The evidence also shows that if children are congratulated for performing well on an easy task, they see it as proof a teacher has low expectations of their ability.
In some cases, if children are criticised for doing badly in a project, they can take this as an indication that their teacher believes in their abilities.
Prof Robert Coe of Durham University said: "Teachers need to understand how a particular approach is likely to enhance students' learning."