The academic who headed the research said the improvements were very much a combination of teaching pupils the appropriate vocabulary, as well as letting them develop their abilities using a computer program.
The software presented pupils with a moral dilemma involving a girl who shoplifted and then told her friend. The study found that children who had used the program used significantly more reasoning words such as "I think" and "because" in later group discussions.
According to recognised linguistic measures, the test groups' power of reasoning and debate quadrupled. Self-confidence and class discipline also improved. The groups took place in science and citizenship classes in three English primary schools.
Neil Mercer, of the Open University's Centre for Language and Communication, said teachers often assumed that children knew how to debate and use the language of reason, but he believed they needed to be taught.
The value of computers in the exercise lay in the way they allowed tasks to be well-structured, while holding children's attention, Dr Mercer said.
The two-year project, funded by the Economic and Social Research Council, was conducted in response to a lack of tuition in language development in primaries, and teachers' fears about using computers in the classroom.