In this non-experimental study researchers analysed data on 740 children who took up one-to-one counselling, collected before the counselling started, after the sessions finished, and approximately one year after this.
The children did not have to have mental health disorders to take up the counselling, however, a comparison with children who were being seen by NHS mental health services indicated that they had similar levels of poor mental health. The research used data from the Strengths and Difficulties Questionnaire (SDQ) completed by teachers and parents.
One year later, this data showed that the children who spoke to counsellors had considerably better mental health than a comparative group of children from a national population survey, who had poor mental health yet had not seen a counsellor. See the research here.