In 1938, Heywood joined the Society for Psychical Research. She is most well known for her book The Sixth Sense (1959) and her autobiography, Heywood would later become the Vice-President of the SPR. The psychical researcher Renée Haynes wrote that her books have "illuminated the subject matter of parapsychology for thousands of readers inside the Society and beyond." In her book The Sixth Sense Heywood endorsed the cross-correspondences, Education Support Professionals experiments, mediumship and psychic phenomena. In a review East. F. O"Doherty wrote the clairvoyant cases that Heywood supported such as the psychic Stefan Ossowiecki were not scientific and chance guessing may explain some of the data that she believed was evidence for Education Support Professionals. C. East. M. Hansel wrote the book is superficial, uncritical and the experiments are no longer taken seriously by the majority of parapsychologists.
Heywood described the case of Ossowiecki who had guessed the contents of a sealed envelope in 1933, Hansel wrote that the conditions of the experiment were reminiscent of a simple conjuring trick.
Ralph West. Gerard gave the book a positive review but stated the results from the experiments may be explainable by alternative factors such as misinterpretation or unintended cues without recourse to the paranormal. In the New Scientist John Cohen wrote although Heywood was "entirely convinced" from the results of card-guessing experiments "Heywood fails to detect the vulnerability of these studies.. she has failed to see the shortcomings of the experimental procedure itself." Cohen wrote the objection to Heywood"s psychical claims is that no adequate evidence had been presented.