Back in the day Dr.Ian Stevenson did studies on past-life regression cases. There's 21 cases which he sums up as good evidence for reincarnation such as birth marks.
This site is also has good information on past-life research. Also at present Dr.Jim tucker is doing reincarnation research
One of the explanations to try and explain the evidence
This simply means that the reborn child had learnt in this lifetime what he is saying about some previous life. The claim is that, consciously or unconsciously, the reborn child must have read the information, or heard about it, or been told about it, but forgotten it.
Dr Stevenson explains that some of the original information from some of the reborn children, especially from those who were as young as two years, was not known to those around the reborn child. From Stevenson's own observation, the child on learning to say a few words would start to talk about his or her previous life. This greatly reduces the other possibilities where the information could have come from.
Another one is fraud
Initially one has to take into consideration the qualifications, the professionalism, the caliber and the integrity of one of America's foremost scientific investigators. Dr Stevenson has a long track record as a highly professional scientific investigator, psychiatrist and psychoanalyst. In addition, years of interviewing thousands of witnesses gave him enormous practical experience in detecting fraud. He himself wrote textbooks on psychiatric examination and diagnostic interviewing.
He says that his interviews and cross-examinations of so many children and witnesses clearly reveal that it would be a gigantic, a Herculean task for anyone to try to organize the situation, the coaching of the parents, relatives, friends, witnesses—sometimes the number involved is over fifty people and even more.
Then there would have to be the staging of the emotions when there is a reunion of the child with the loved ones of his former life. The staging of the intense emotions of these situations is outside the human capacity to structure 'on site'. Having interviewed thousands of 'reborn' children, Dr Stevenson adds that, 'small children are not easy to coach for the assumptions of the roles that do not seem natural to them'.
Stevenson publicly stated that he does not give money to any of the people involved and consistently applies his policy that no payment is to be made for any testimony. Nor is publicity given as some incentive to co-operate.
Dr Stevenson has always been fully aware that the scientific investigations he conducted would be scrutinized in the minutest detail by other scientists, by outsiders and by those with vested interests who would not want him to succeed and who would try to denigrate and undermine his scientific investigations into the afterlife and reincarnation.