arallel Parenting was first observed in the sandpit. Psychologists noticed that without the skills to socially interact, young children played independently, side-by-side in harmony. As neither child hit or bit the other, psychologists decided that this model of behaviour should be adapted to parents in the aftermath of a nasty divorce - the idea being that parents can co-exist without conflict, providing strict rules are observed. Of course, other psychologists then came along and said that parenting is not like playing in a sandpit, and kids behave better than adults, anyway.
Parallel Parenting is not unlike job-sharing, where two individuals, who would never have played side-by-side in the sandpit, are asked to co-manage and co-share in any future successes. In most cases, it leads to what psychologists now call the 'conflicted model', where one member of the job-share promptly fails to do his/her share of the work, but till takes all the credit.
Job-sharers don't exactly hit each other over the head with a shovel, but it's pretty close.